How do i deal with my sister who wont help pay her share of the rent?

i live in a hotel next to were my dad and sister and her 5 year old terror live .and my dad is having to pay for his own room plus my sisters room and now she has a boyfriend who is staying in the room with her. my dad is having 2 pay 4 her ,her kid,and her boyfriend plus his own room,and they wont help pay a dime, she said her bf get 14.00 an hour catering but i thinks its a lie. and if thats the case why arent they helping my dad.she thinks just cause she gets 300 a month means she dont have to pay rent. my dad is gonna forfeit his room monday or tuesday, cause he cant pay for everyone anymore. now im moving my dad into our hotel room with me and my boyfriend till he can find a place. my sister has been cold shouldering me and now this is happening. she thinks everything is a competition, and thinks everyone is jelouse of her looks.she always talks about her past when she was a pole dancer. and talks about doing it again under the table. she is 37 acting like 15. and my dad(our dad) is 65, and im 18.i dont know what to do to her. shes convinced she cant get a job because she has lime desease and is on food stamps and taniff. and now she has a boyfriend. she accuses me of things that go wrong and says i dont care about our dad. but really i dont think she does. i need to know what i could do or say to her to wake her up any suggestions?