It sounds as though your son has unresolved issues from his childhood; perhaps his wife does too. 4 children is a lot to handle - and probably more difficult because of the parents' issues.

I'm actually not surprised that they take no responsibility for what the oldest son has done. In the long run, being locked up might be the best thing that could happen to him. Yes, know that sounds strange - but he is now in a place with structure, rules and hopefully counseling, etc.

It is possible that the wife stops you from seeing your grandchildren because she feels lost and scared and is afraid for you to see her during those moments. If you feel that your mother is taking sides with your son - why not sit down with her and ask her questions to find out why? With age comes wisdom - perhaps she has a perspective on the situation that you aren't able to see right now.