How does one keep sane with a father who is blinded by his daughter and her chldren who take advantage of him?

My younger sister has always been a taker of many people. She would use her problems created by herself & her young adult children to seek out others to take care of situations that come up by asking for $$, food, gas,etc.She is currently living in my parents home with her adult children and my father will not put them out for he feels as if he has failed her when she got divorced.?? He has been paying not only for them but her 2grdkids too who stays 2wks out of the mth.Their father is never with them &comes to visit them at night only about 2 times a week&than asks my father for $$ or to pay his rent/bills.He works but spends his $ on not the right things.My sister decided when she moved in that she would cut her work hrs and help out taking care of mom who has alzheimers.they yell at mom all the time.I work an 8hr day,I clean moms room,wash her clothes,cook for both give meds I do this before work&when I come home.She spends her $ on bingo.My $$ buys mom things she needs. I feel lost