I Have An Inclination, Need Some Help

My sister I beleive is having issues. She is 30 yrs old with a 4.5 old son. She lives with her her husband, child and mother in law. She treats everyone very badly at home. Always wants to argue, fight. She picks topics that are years old and keeps fighting with her husband. gets violent, throws around things, has become foul mouthed and talks very badly with her mom in law and keeps beating her child. I have an inclination that she needs help but has a weak husband who to avoid confrontation does not say anything to her. she stays at home the whole day without social activity around. Only cooks for herself and her child, sometimes not even that. I think her husband is one of the best guys that she could find but does not have the guts to take her to a doctor . she always tries to aggravate everyone to fight with her. Her husband obviously does not think to take her to a doc/psychatrist because hes too scared. what to do ?