I agree with Rose on many points.

I don’t think mother needs to be in their house showing up unannounced. She doesn’t live there.

But if visitations are properly established, DD has rights to see her mother.

I don’t think it’s up to her brother when and if DD sees her mom. Kids typically have rights to maintain contacts and see their parents (in the absence of abuse and court orders prohibiting parents from seeing their children).

Even if for whatever crazy reason it was decided to let mom visit DD in the house, it’s not up to him. If he doesn’t like it, he could go somewhere for the timing being so he won’t see mom but he can’t make these decisions.

I think it’s a but ridiculous for him to say that he won’t have any contacts with anyone who talks to his mother. Like why?

So he’s threatening a child (I assume she’s not of legal age) to cut her off if she’s as much as talks to her mother? That’s highly inappropriate. It puts a kid in a bad situation. He needs to be told to knock it off.