magneto you poor love. What a massive amount of stress at once. Regarding the work situation of your two BILs and sister, that is something they must sort out for themselves. Hopefully, the fact that there are three of them could increase their chances at a good outcome: for example, they could all report problems to the police (hope BIL who was assaulted does!). Or they could put pressure on the company to find a solution for their safety. or they could band together to enter and leave the building... There are plenty of possible solutions, and it is for them to seek those solutions, not you. You just take care of yourself, and your own decisions, and be there to listen to them and provide comfort if they want it.
Regading your mother, I fully understand you and your siblings not wanting to be involved in her hospitalisation and after-care. You did well to speak to the nurses, if that is what you wanted to do for yourself. But you do not owe it to her to fix her, placate her, or find solutions for her own MH issues.
My own mother has apparently been threatening suicide to my sister, and it makes me boiling mad that she would stoop to such manipulation. If she ever does attempt anything, I know I won't be pandering to her by sitting by her bedside: I would be too angry.
toughday you and your DH can each have your own relationship with his parents. If he's not ready to cut them out of his life, then he's not ready to cut them out of his life. However, you can cut them out of yours, if that's what you want. And you do not need his permission to call his mother and tell her how you feel, again if that's what you want. Although be warned that toxics will not take your feelings on board, and anything you say will only be used against you...
Have you read "Toxic In-laws" by Susan Forward? It might help.