Well, as the wedding drew near my wife's dad decided that her marrying this doosh was not a good idea and he tried to break them up. He went so far as to beat her severely with a belt all over every inch of her body.
he said that there is no such thing as mental illness. All crazy people are possessed by demons.
You can't fix crazy.
As for the beating, seems like there was a reason your wife chose to marry an abusive first husband, and it's great she chose wiser with you.
I support Quandry's advice, when you're stuck associating with crazy and abusive whackos, life looks bleak whichever way you look and you can never imagine for you, your wife and your kids to ever get better. Then when for a reason or another you get out of the hole you're stuck in, your view of life completely changes and so does that of your family members. Especially with the intense pain your wife has, that's to strong for medication to have a notable effect, a brighter outlook and not being brought back to depressing situation does wonder. Hospitals notice significant decrease in pain medication and patients reporting less pain when engaging in clown and comedy activities, and I can confirm from personnal experience (living with crazy, then getting out is also something I can confirm ;) ).
I really hope you can get out, especially since the situation weights on you. Sometimes, even though you love the people (talking about your in-laws), they're really ruinning the life of anyone close by, and only having nobody around to complain to will give them the kick in the butt that makes them realise they ought to get a fricking life.