"Happy" Holidays....Yikes!

This is my first holiday season as a caregiver. Normally my children and I visit for a couple of hours then race home, THANKFUL for the peace and quiet. But now that we are living with my 87 year old father things are very different. Im trying my best to make things happy for everyone. But I feel like its never going to work because of Dad. Perhaps its wrong to blame him but hes the one who ruins all good moments in the house at this point. My sister has been here since last Saturday. He is EXTREMELY POSSESSIVE of her. He got angry at her the other evening because she was spending time with my daughters rather than talking to him. She sits right next to him all day..right up until he goes to bed . She listens to him, listens to CDs, watches Movies. All he does is sit and complain about me, my children, my brothers.
He is treating me very horribly. Talking to my sister and completely ignoring me or giving me orders. I offered to make Thanksgiving dinner. Of course he is sabotaging that. He had to have the HHA take him to the store to shop so that he can announce to everyone what he contributed.
No one wants to be around him at all. Hes an angry, bitter old man now and you never know when the next explosion will take place. At this point its like living with a spoiled toddler. If you dont pay attention to him, he throws a fit. You cannot watch a movie, play a game or even talk without him taking over the conversation...directing it to my sister. ..Then turning it into an argument.