I can't stand that my brother in-law and his wife have everything good going for them
Why the resentment towards them?
I think my wife's brother is an asshole who always takes advantage of her sister.
I think it's better if you focus on your life instead. You can be sure their life is full of ups and downs just as yours is.
I want to shake them until they come to their senses.
What your brother-in-law doing with his life shouldn't be your concern. It has nothing to do with you. You should think about yourself and your family.