Difficult brother in law

Bit of background sorry for the long story. My husband comes from a difficult background, alcoholic mother, absentee father, endless parade of increasingly violent and abusive "step dads". With many many years of support from myself, a good group of friends and a little bit of therapy he has been able to resolve many of his childhood issue's, thats not to say he is perfect but he tries everyday to be a better person and parent then the examples he was brought up with. Unfortunately the same can not be said for his brother. We have both tried to give him some help and support, but there is only so much you can do for some one that thinks nothing wrong. Over the past few years he has become increasingly withdrawn and depressed. In the past I have encouraged my husband to make sure he gets out of his house every now and then and interacts with people. Lately he feels he needs to drink A LOT in order in be around others. When drunk he turns from quirky recluse into an aggressive inappropriate nightmare. To the point that I will no longer allow him to be around our children when he's had anything to drink. I have tried to talk to my husband about it but his automatic response is always to defend his brothers actions even when he has touched me inappropriately or accidentally hurt one of our children. His usual excuses include, oh I wouldn't understand, or thats just what he's like, lately hes been saying that he's got enough responsibilities as it is without taking on a father role to his brother. I am now at a loss of what to do. I would hate for him to hurt himself or someone else, but I have my own little family to think about. We are not responsible for him or getting him better but on the other hand my husband is all he has. What should I do??