Trying to diffuse a hostile environment.

Major conflict with grown children regarding Mom. there are 4 children in my family. Not all of us have had a positive impact in our Moms life. My father passed away in the early 90s and none of the older children stepped in to ask or help our Mom. they were more concerned with a will & what was left to each of them than making sure she was ok. Fast forward to about a decade ago. The brother lives in the same town as Mom. He has an odd relationship with the older women in our family - tends to get them to financially support him & he is a bit mean towards them all - & when he can't gain anything from them anymore he washes his hands of them (several instances of malfeasance when he was supposed to POA for these women). He had a disastrous marriage - wife became tired of financially supporting him & during the time when the marriage started to fail, he began borrowing money from our 80+ year old mother (who is on limited income). Also during his time period, the oldest sister( will refer to her as A) was off doing her own thing - did not & does not financially contribute to Moms life. The second sister (call her B) was involved in Moms care - but only to the extent that Mom would ask for(she's since majorly stepped up her involvement) . I, however, have always been closely involved in ALL THINGS related to Mom's affairs, some situations I was not made privy to until after the fact (when it was too late to fix any problems that were created by lack of knowledge). However, I did the best I could with what I could ascertain. about 4 years ago - Mom let it slip that the brither had borrowed thousands of dollars from her (to prevent insolvency - he put that in writing!) & I asked my Mom to speak with her attorney about it. Additionally mom was diagnosed with major neurocognitive disorder (I found this out when I was switching her health insurance - the brother knew & told no one. Mom should've been taking the prescribed medication & was not- not until I found out). So at the meeting w/the lawyer, I told her everything I had learned about the money/loan, the diagnosis, etc. It was at this then I learned my Mom had made me her POA. The brother had been POA (while taking $$$) but Mom changed & made him my back-up. The attorney suggested removing him completely bc of the "conflict of interest" and possible undue influence & added sister B as my backup. Additionally, Mom wanted her will updated to reflect the money owed her & that it would be deducted from any inheritance he could possibly receive. Additionally, we discussed the possible future need for a guardianship. Mom stated she wanted a co-guardianship w/sister B & me (primarily because both of us have professional backgrounds & personal relationships w/Mom would be best suited for caring for her. both of us are far more stable than the other two). Unfortunately, the updated paperwork was sent to Moms house - I'm almost positive the brother & sis A read it (or brother saw it and told sis A). From that point, there has been major dissension w/the kids. They fight everything I put into place. I've found out more has been going on (forged signatures on checks/credit card slips), reckless spending of Moms $ and brother & sis A are indignant towards me. Mom is now living w/sister B (for 6 mos). Brother assaulted sister B - protective order is in place, he was arrested & case is pending. I've petitioned the courts for co-guardianship - hearing is in a few weeks. Brother & sister A have not seen Mom since the assault happened. Sister A wants nothing to do w/sister B, and now wants Mom to stay w/her for about a week. Mom wants to see sister A but does NOT want to be w/her for more than an afternoon. Mom told sis A to call sis B to make arrangements. Instead sis A sent an odd email instructing sis B if what she is to do. The info isn't specific (things like - bring Mom out to the curb in front of your house. Don't know when I will be bringing her back or where she will want to go...) so Mom declined the invite and called her to say so. Now sis A has written another odd and hostile email to sis b - claiming that she's brainwashed Mom and that it's not Gods will (?), there's a veiled threat in it and that she's still coming to pickup Mom. Hostile hostile situation. I've asked sis b not to respond. I'm sending the letters to our attorney but don't know what to tell sis B. I don't want sis a sitting outside of sis b's house. I don't know how to diffuse the situation. I truly believe mom doesn't want to be subjected to an uncomfortable visit with sis a (they've not ever been close and these kinds of trips never happened before). Should I instruct sis A that she need to consult with her atty who will contact our atty regarding this matter as to avoid misunderstanding/miscommunication? It's like a child custody case & im hoping this type of matter will be resolved at the guardianship hearing/when it's in place. Very complex matter.