This is a terrible situation, but not uncommon. I'm surprised APS hasn't been more aggressive. A couple of options would be: (a) a Power of Attorney and/or becoming Trustee if they have a trust so that brother has no access to finances; (b) a conservatorship for your parents to control other aspects of daily living. I think if you take away his access to resources, you will go along way to bringing his behavior under control. If not, then your parents may need to get a restraining order against him. But if they allow him to live there, then problems will only continue.
