Does this seem odd to anyone other than me?

Maybe she thought with minor children this would be asking to much. I would just sit down and have a heart 2 heart with her, find out what her views on this are. Sometimes when we speculate about the "why" of things, we are so far from the reality we feel silly when we learn the truth. Try not to be unkind to her with an audience, this is a sure fire method of creating hard feelings, as you yourself expressed after she treated you the same way. One thing about family is you can forgive and let it go if you choose and not have to think about saving face.

Best of luck getting this resolved.

The thing that jumped out at me about SIL giving control of your brother to her family, uhm, how exactly is she doing that? You can't hand off POA or inherit it, and I'm pretty sure she wouldn't be allowed to bequeath her assets to her sibs thus leaving her dependent husband destitute and dependent on their kindness.

Yes, it seems odd to me. If something happens to one spouse, it seems only natural to me that care of the surviving spouse would be handled by the relatives on that side of the family. Unless there is a need that clearly cannot be met by those relatives (which doesn't seem to be the case here) I cannot understand why your SIL wouldn't assume those on your side would be in the best position to oversee your brother's needs. At the very least, you should have a pivotal role in decision making. Just my opinion.

I think it is time to see a lawyer or counselor for some advice.

Oh Suzee I am afraid that my advice in this kind of situation is to follow the money.
SIL does not want you and your family to get your hands or any of your family on your brother's money should she die before brother.
Definitely see a lawyer for advice. In the event there is no POA which of course your brother has to give should he be competent. As his wife she has authority during her life should he need someone to act for him.
I just went back and re read your post and it seems that you had the suspicion that SIL was protecting her assets was her motivation.
My concern would be about the comitment of her relatives to properly care for your brother. If SIL does die prior to your brother you will have to be very vigilant about his care. In the worse case you may have to seek guardianship if the worse comes to the worse.
I can't comment on whether the friendship you enjoyed with SIL was real or not or if something along the way changed things. Only you can answer that question.
What kind of disability does your brother have?

Well, as they say, "to assume makes an ass out of you (u) and me". You made some assumptions about her motivations in naming her family members as POA for your brother. It probably would have been better to ask her more about her trust levels and why she trusted her family more than your brother's side of the family for his care. Is your brother mentally or physically incapacitated? If he's mentally ok, I would think he ok'ed her choice. But again, can you get him aside to talk about it? I know that can be difficult, my SIL and brother were like one person - I could never see or talk to him alone. So I know how hard that can be.

You've taken some actions that have created a difficult relationship. Your gut feelings may or may not be true, but the only way to really find out is to talk to your SIL about it. And if you want a decent relationship with your brother, you may need to put aside your feelings and be cordial to your SIL.

Are your children still minors?

Is your BIL's disability such that he can't make his own decisions? Has he been declared to be incompetent? Is his wife officially his legal guardian, appointed by the courts?

When your SIL dies, her will will be probated. Her assets will be distributed as she specifies. It could be to her husband, her relatives only, the national society for the welfare of homeless cats. Anything that she alone owns can be given to anyone she wants. This would be true whether her husband was disabled or not (I think!)

The will can also state who she thinks should be guardian of her husband (if he needs guardianship at that time.) Unless there are reasons not to or someone objects, the judge will appoint that person. If there are objections the judge can investigate and assign the guardian role to someone else.

I'm not sure why you mentioned that they are weathy? Is this mostly about money?

Guardians are required to use the ward's assets for his care. They must keep detailed records and report to the court. They wouldn't have total control over everything. There would be supervision.

Is your BIL able to say what he would want?

It is my understanding that depending on where you live you can't just willy-nilly disinherit your spouse or any dependants, a common assertion on many legal website is summarized by this statement
"you should be aware that many states "protect" spouses with laws that permit a spouse to receive a portion of the estate even though the last will does not provide for the spouse."

Jeanne also says "The will can also state who she thinks should be guardian of her husband (if he needs guardianship at that time. Unless there are reasons not to or someone objects, the judge will appoint that person. If there are objections the judge can investigate and assign the guardian role to someone else."  Yes, and if you are capable and wish to you can make your case that a blood relative who cares for your brother should be given consideration above his in-laws.

@isthisreallyreal - yes, I think you make a good point. And, now that you write that, I'm reminded that she did briefly mention at one point many years ago that I had a lot going on when she make these arrangements. So much has happened since then - lots of illness, loss and death in our family. It still seems strange though, that not one of us would be asked to be part of the decision making team in regard to our brother. Chances are, given his state of health, he won't outlive her. But, life is strange. Anything could happen.

@cwillie - I don't really know. All I know is that she said she set everything up so that if she goes before he does, he's going to be an extremely wealthy person. He is not in the position to manage that, as his post stroke thinking has left him with focus and impulsivity issues, to put it mildly. I don't want her stinkin' money. I am uneasy, however, with non blood family members making life decisions for him.

@GingerMay - there are absolutely people in his family that are fully capable of caring for him. And that's exactly it - I think that someone in his family should have a 'pivotal role in decision making.'

@bharty615 - Good idea. I will be making an appt with an attorney for another matter, and will bring this up as well.

@Veronica91 - I totally agree. As long as I've known her, she has been extraordinarily focused on money, almost viciously so. My concern also is whether her relatives would properly care for him. My father has put me in charge of his trust, and has made it ironclad tight so that no one but me can touch it, even after his death. He put pretty strict parameters on how the money can be spent. I'm almost positive he did that in order to make sure his assets that are set aside for my brother, will go for my brother's healthcare, or wherever it is most needed to help my brother, and not her bank account. As a married couple, it belongs to both of them, but she is a bully, to put it bluntly. And he does whatever she wants, whenever she wants.

@blannie - I wish I had thought of and had had the courage to be so blunt with her at the time she told me. It's not the right timing now. I doubt she'd give me the time of day. My brother is mentally and physically incapacitated. He can carry on a conversation, but cannot work, or do any sort of record keeping. I guess you're right - I HAVE taken actions that have created a difficult relationship. This is a recurring theme between me and my family. They have the habit of steamrolling over me, and negating most of what I say (this is not an exaggeration), and somewhere around 40, I stopped being complicit with that arrangement. I guess when I realized what the relationship dynamics were, and how unfair and unhappy I was in that role, I didn't really know how to gracefully get out of that pattern. I thought I was being graceful and non threatening, but I seem to have really offended people. In my defense, there were many things that I said, that were completely in line, but were ridiculed and sneered at. Like when talking about another family member I once said something like, 'if it were me that was diagnosed with stage 4 pancreatic cancer, I'd want to get a second opinion,' AND 'I would like to ask you to please, please contact me before you give anyone advice to put my mother in hospice,' OR 'most people don't react this way to the type of surgery that mom had, can we get a second opinion?' ALL of the statements were met with anger and ridicule. It still doesn't make any sense to me at all. But I agree. If I want any sort of relationship with my brother, I have to be cordial to my sil.

@jeannegibbs - No, my children are no longer minors. My brother's mental capacity is hard to gauge. He's a quick wit, but can't figure out simple math, and has no patience whatsoever for seemingly mundane tasks. He definitely needs 24/7 help, but is certainly capable of deciding how he'd like to spend his time, for example. His common answer when asked about his thoughts is, 'it doesn't matter what I think, she calls the shots.' He's not being a martyr when saying this, he HONESTLY believes it doesn't matter what he thinks. I guess I mentioned that they are wealthy because my suspicion is that money is the motivating factor behind her decision. Good to know that there are some checks and balances for guardians. To be honest, after raising kids, caring for parents and grandmother, I don't really want primary custody of anyone else, but would like for someone from his family to be in on helping him make decisions, or helping to make them on his behalf.

I don't know why this has been so difficult to articulate for me. I get tongue tied every time I try to talk about this. It's as though the issues of the heart and mind have become so tangled up into one big mess. It helps to write it out, and to read your comments. I can't thank you enough for walking down this path with me.