What rules in the TOS are they breaking though? You can't just have them banned because you don't like them.
If they're just standing in a public location that's not really harassment either unless they're blocking something like an NPC or an interactable object.

The solution would seem to be to move your venue indoors and modify the permissions on the house to not allow them to come inside. Other than that they're really not doing anything wrong for existing in a place you don't like. If they aren't saying anything abusive, their names aren't abusive, and they're not blocking anything important then there's not much a GM could even do.