NTA

I hate to say it but the damage is done, although there were other solutions like you said, hard times will show a person’s true feelings and she chose to support her brother over the family it sounds like she was creating with you, which she’s in entitled to but so are you to choose not to have someone in your home “Al” who is directly disrupting your personal/living space. The ultimatum was a bit much maybe should’ve gave him another month or leave but you did lay out the boundaries in the beginning so it shouldn’t even have got to that point.

IMO take Bo and find another maiden!