Too much?

I guess my issue is a bit different. As a preface I want to say I love my family more than life itself. Now to the nitty gritty. About 8 years ago my grandmother's grown sons moved into her small home. They never paid rent, forced her to give up her car to them and pretty much treated her like garbage. It all came to an end when she fell and broke her knee. They threw her in a nursing home and said she was too much to deal with. Mind you she was still working and supporting these rotten individuals. I lived a bit away, but decided to step in, so I moved her to my two bedroom apartment and the rest is history. She no longer works and lives comfortably with me. Which I have no problem with. Fast-forward to Dec. 29th and she has to have the other knee replaced (a long time coming procedure). I took the day of the procedure off to be there for her. They release her two days later, to my sister. I was fine with that because I had no other options. My boss is strict about time off. While I am at work they make the decision to stay at my sister's house while my grandmother recovers, the catch is they have to keep my car because they only have a van. So I am left with no other option but to crash at their house as well. The only problem with that is they have 2.5 bedrooms. I add the .5 because the room my grandmother is in is a converted study/playroom. One of the rooms belongs to my sister, her husband and her 6mo son. The other room has my other two nephews. I'm left typing this on their couch in the living room where I've been for nearly 4 weeks. I know some may say to just go home, but I would feel guilty leaving my grandmother to someone else. Especially my sister who ignores her appointments and half heartedly "takes care" of our grandmother, she has really dropped the ball several times in the past four weeks when it comes to my grandmother's health. I guess my problem is I haven't slept a good night's sleep in four weeks due to the constant coming and going of everyone, plus I have no time to myself. I'm just over stimulated and I am desperate for a break. To top if off my sister is very spoiled, her husband allowed her to become a housewife, that does nothing, and when things don't go her way she throws a tantrum. I have to literally sit by and listen to her throw fits over simple things. The room is always so tense because she is like a time bomb, you never know when she is going to go off. I'm typing this today because first thing this morning she got upset that her husband pecked her goodbye instead of locking lips with her. Then took it out on all of us, and when we didn't acknowledge her it got worse. She finally asked me why I was so tense and I explained that she was being very hateful to everyone and when she asked the room how everyone if they felt the same, they said yes, so she stormed off to her room and refused to talk to anyone. She us treating me like a leper. I don't know whatelse to do. I do apologize if I'm rambling or if it seems like I'm whining, but I'm just lost.