Im really worried about my younger sister..?

okay im 19 and i have 2 brothers and a sister. my younger brother Jake is 15 and my younger sister Jessica is 14 and are baby brother Kenzie is 2.. are mum died last year of cancer and she was the bread winner of the familly and since she died my dad hasnt been working and he's turned to drink + drugs.. I have a little boy myself who is 1 who is called Josh.. As i am 19 i am old enough to move out so shortly after my mum died and my dad started drinking i did, i knew it wasnt a good environment for my brothers and sister even my own child so when i moved out, my 2 brothers and my child came too leaving my sister. i work but i do not make alot of money and i dont get alot of benefits, i litrally have no money.. anyway last saturday my brother said he'd babysit as he's 15 and he's on cerfew with the police atm so cant be out later than 7, so i went into town and it was 3am and i was on my way home and i see this girl with 2 guys carrying her and throwing up everywhere with a big bottle of vodka in her hand, and i remember thinking '****, feel sorry for her brother' and she looked up and thats when i seen it, it was my sister. of corse i went over and helped her and i carried her back to mine. and i put her to bed and i just sat there in the dark and i just couldnt understand how everything had ****** up so much.. i mean i remember are whole familly sitting down for are familly dinners laughing and smiling and now... anyway in the morning i thought d go over to my dads to ask why the **** had Jessica been out at 3am and he didnt even call.. so i walked down and the door was open so i go in and there's drugs and alcohol bottles everywhere. so i thought **** it im going, and as im on my way back i see my dad sat outside the pub still drunk and drinking and i just walked on.. i dont want anything to do with my dad anymore but i feel like such a **** for it. and i know i shouldnt let my sister live there but i have no money. im broke, i just thought when i left she'd be alright because she was the strong one and the whole time mum was sick she didnt cry once. but after spendidng the day with her i've noticed theres no compassion or caring anymore in her heart, its almost as if shes been hurt so much shes stopped caring.. i dont know what i can do anymore?