How to choose sides in a divorce?

My sister-in-law got a divorce. While I had a great relationship with her ex-husband (as far as I was concerned, he was a great guy), when the process moved forward, I had no choice but to be on the side of sister-in-law. I had to stop all communication with him because having even a casual acquaintance with him would have hurt my sister-in-law. A few years later they have a horrible relationship and often face problems while raising their 3 daughters. Sometimes I just wonder if I could pick up the phone or have a beer with her ex and help him better deal with the problems that they have because they do not even look at each other any more (they only communicate through their children). Here is a great video of Jill Brooke and Julie Chen that talks about divorce and relationships without choosing sides.