My moms says this was the method adopted in olden days in joint families if there is a mentally sick/insane family member. Deny all their verbal abuse and craziness. So they can have a socially acceptable life. I have to wait for the craziness to come out in open not just family. Till then avoid like you would a rabid dog. I don't think me yelling or showing anger will change an iota of what BIL does, rather increase it as it is a trigger. If I stop him fro coming to the birthday,he will just do triggering over phone, and husband will ask innocently, can't I even talk on phone with my brother?