it's quite natural for your son to have these feelings. He is obviously feeling defiant towards you, and however bad his father has been to him and his brother, he knows that his father will do anything to try and win his acceptance. He wants to be the 'cool dad' so don't let him put you down you have obviously worked hard to bring your boys up. But because your son is 16 he is entitled to see his dad if he wants . The best advice i can give you is just to lie low. It will be hard, but at 16 your son is old enough to make his own mistakes. Try reverse psychology let him stay over at his dads. Your son will be confused with you laidback attitude and his father won't tolerate it if he takes advantage. Then your son will see just how much he appreciates you.
Hope this helps
r xx