I think choices have to be made by your aunt since she is physically abusing your aunt and so much larger and stronger. That cannot continue. I think force will have to be used to remove her from being able to hurt your aunt and to provide any hope of getting her into a better frame of mind. Her friends and running the streets and doing illegal drugs can only land her in a worse place? I think your aunt should take the chance of giving your sister a last chance and if she doesn't straighten out, she will have to let go of her for now; she's too old and "strong" to control by parenting at this point it sounds like.