Yes, they live together. One of the reasons A was flipping out (beyond the obvious) is that she isn't supposed to leave mom alone. Turns out it's mom's apartment and she offered to have the kids move in since they were checking in on her most days of the week.
We don't know them well though we've known them for many years, just small talk in the hallway or elevator, giving us some dog things when theirs passed away. A didn't know my name until the other night.