Cant handle inlaws.

I have posted about this so much already but its getting worse and i need to rant. I cant handle my boyfriends little sister. She absolutely drives me insane she doesnt even let me have my own child. She is 12 years old and acts like she runs the whole family. She bosses her mum about and her mum does everything she says, she has no manners and thinks my baby is hers. We live at her house so i cant exactly tell them what to do in their own house, but my boyfriends mum is actually scared to tell her to stop and when my boyfriend tells her, the rest of the family abuse him for being horrible to the 12 year old cause shes "only a child". In the mornings she lets herself into my bedroom when im asleep and takes my baby and takes her downstairs. She doesnt let me feed her because she wants to because its "fun" she gives her sweets to suck on and food shes not aloud to have (shes 6 months). She swaddles her when she hates being swaddled and my baby cries when she holds her. I literally try take her back asn she walks away with her sayint "its fine i got her". She has at least 3 days off school a week because she doesnt think its fair how i (her own mother!!) gets to be with baby all day and she doesnt..!!! Earlier she sat her on the floor when i was in the kitchen, she wasnt watching her and my baby fell and hit her head on the glass table. I pushed her out of the way and snatched my baby back and walked off. APPARENTLY I AM IN THE WRONG BECAUSE IM NOT FORGIVING HER. I said i dont want her holding her anymore and apparently i am being unfair. UNFAIR. I would rather be homeless than live here anymore.