New here and don't know what to do.

A little background info on me and my father. I'm 27 years old I have 3 children who range in age from 3-7. My husband and I have been married for almost 9 years. My father, who is 63, was diagnosed with FTD (frontotemporal dementia) about 6 years ago. My mother was his primary care giver. In 2010, while my husband and I were stationed in Italy with the Army, my mother passed away from ALS. My husband got out of the military in October 2011 and we moved back stateside in order to care of my father. We all currently live in a 3 bedroom home in VA. Most of the time I feel like I'm going to lose my mind when dealing with my father. I try to be respectful of him while still setting boundaries. It's really hard. When I tell him no or I question the things he is doing or wants to do he gets very angry and mean. He curses at me in front of my children, he yells at my kids for no reason, he's rude and impatient all the time. The more I tell him no the nastier he is with me. If I question him he gets nasty with me.
My father still has the ability to drive (god help me) and wants to take a road trip to a battle field 3 hours away. He says he has a map and can drive himself. I told him that I'm sure he could but I wanted him to pick a place on the map, any place, and drive me there 1st. He got so angry with me. He said I was calling him stupid and I was disrespect and ungrateful and some other choice words. I know he can't do this because I have given him simple map quest directions with a map to a place not even 5 minutes from our house where he knows all the roads and landmarks, and he couldn't find the place and ended up getting lost. I've tried to explain that I question him not because he's stupid but I need to make sure he can do these things for his own safety.
There are times where he asks me for help with something and the whole time I am helping him all he does is yell at me and belittle me. I'm finding it harder and harder not to lash back at him. the other night he wanted me to bid on something on e-bay for him and he yelled and cursed at me and the computer for 10 minutes until the timer finally ran out and he won the item. after it was all done I said you know Dad normal people don't act like that when someone is helping them. There was another time where he was cursing at me after I had helped him find a phone number for someone and I yelled at him to stop acting like a mean old man. Sometimes I feel bad about the things I snap back with, but he just pushes my buttons in just the right way that I snap.
He doesn't understand why I I won't let him spend his own money on things he wants. I bring up the fact that he just spent $40 on an ancient ( late 1980s) camera at goodwill that doesn't work and that he ended up throwing away. Instead of cutting his losses and saying oh well he went on e-bay and found the exact same camera and had to buy it to replace the once he bought at goodwill that didnt work (WHAT?!?!) So instead of paying $40 for a POS camera he has now spent $80 on 2 POS cameras (hand smack to forehead)
If he needs or wants something....no matter what I am doing at the time he says I need to stop it and help him....and he will stand about 6 inches from me cursing at me under his breath until I come with him.
I do all the cooking and cleaning for everyone in the house. All 6 of us. We have a very strict grocery bill so I trying to stretch dinner over a few days. For instance, the other day we had baked chicken, sauteed cabbage and mushrooms and brown rice. We had leftovers so the next night for dinner I made chicken fried rice by combining everything some some frozen mixed veggies, soy sauce and scrambles eggs. I give my father whatever is left over from dinner for lunch the next day. Today, he looked at lunch, gruffed, and said something under his breath. I asked him what was wrong and he said you make this too often. Granted I make it about once every other week...but its cheap and easy and fairly healthy. He does this with everything I make...either he says he doesn't like something (chicken, steak, fish, rice, veggies, ect) or he says I feed him too much or too little (I feed him the same amount every time...I actually measure it out on a scale) When he goes out and buys a candy bar or ice cream he'll blame me for his sugars being high. If I gives my children a treat he gets mad if he doesn't get one too. Ive tried explaining that hes diabetic and can't have what the children have (usually a cookie for good behavior for the week). I think hes mad because I wont let him eat junk food all the time. My husband and I are very health conscious and we don't eat any processed foods. I make almost everything by from scratch. Since my father has moved in with us he has lost 50lbs (from 280 to 230) has been taken off his diabetic and BP med and we're slowly working on getting him off his cholesterol meds.
I just want him to appreciate what I do for him and I know he doesn't and its frustrating.