Hi Rachna ,
Your sister is very smart and clever but shows intelligence in the negative. She does not get along with your father or anyone else in your house. As far as support is concerned, her marital life is good and her husband is her great support, although they have fights there too.
The tension in your house due to your sister is not likely to reduce now, on the contrary, it will increase day by day. You just take care of your father, his mental and physical condition may improve, then this thing will start reducing a little bit on its own.
As I said earlier, it is not possible to write so many things here nor is it right.