You can set new boundaries with them too you know. When they bring up your mother you can say "I prefer not to talk about mother, tell me more about how YOU are." or something of that nature. If they persist, end the conversation. In a nice way of course, but they'll get the hint. It sounds like she's using them to send you messages, so even though she supposedly isn't talking to you, she's still making sure to get her point across.

That's her choice. It is sad, but ultimately she's the one that decides what to do. If she ends up on the street, she's certainly chosen that. I'm sorry you're going through all this!