I’m so sorry, Natalie. No, it’s not your fault at all and I can’t blame you for feeling shocked and possibly confused. I don’t have a clue what they think they’re doing, but none of it’s fair to you (granted, your brother doesn’t sound fair/rational anyway). Your friend is out of line, too. I don’t understand why we get told to forgive others for choosing to hurt us? If there’s an apology, remorse and steps taken to prevent it happening again, sure, but even then it’s a privilege, not a given.
Above all, you have the right to not be responsible for where your brother lives if/when his wife divorces him. He’s an adult, he should work it out for himself.