I have boys that are the same ages. We have been dealing with the same issues. I have just started a chores chart things like brushing their teeth, making their bed, helping with laundry, and playing nicely with your brother. They can earn stars, after so many stars they get a treat. My treats include reading a special book, watching a movie or cartoon, playing with playdough, anything that they enjoy to do, but not as often as they would like. It has only been a few days, but they love trying to earn their stars. When I see that their behavior is acting up, I remind them about earning their stars.
Divorce is difficult, so many changes, they will continue to act out, but maybe lots of rewarding will help them out a little. Hope it helps!