So let me get this straight:
You, your son, your sister and her partner (and dog) are ALL living in your mother’s house?
Your mother is at her wits end trying to cope with the constant dramas?
You earn 40k per year and you can’t afford to live somewhere else?
Puh-leeze…gimme a break! Move the fuck out, ALL of you. You are all blood-sucking leeches living off the goodwill and mental health of your mum.
Stop playing the victim-card here: you are responsible for keeping this melodrama happening. Your sister might be a psycho (maybe) but you are just as mental for prolonging it. The family dynamics here sound way-off, but to be perfectly honest, it also sounds like you are getting into the martyr groove by whingeing about Teh Evil Sister (whilst forgetting about your own selfishness).
Move out. Get gone. Leave your mum alone,
ALL OF YOU. Geez :rolleyes: