Do not, please do not give your son any books to read. I did that, learn from my mistakes. At this time your stbx is playing dad of the year. (probably). The father they always wanted. It will all bite you in the a$$ to do this. Another thing to remember is that while they were growing up, they might have been afraid to express their emotions to him, instead they probably went to you. (I may be wrong here, but don't think so). So since you may have been the one that was there so that they could talk to, they aren't really afraid of taking out their emotions on you right now.
I may be wrong here, but think about it.
Don't push anything right now. You can let them know that you love them and will be there for them, then stop at that.
(((((((((((hugs)))))))))))))
amy