I understand, sense. In my big break-up, I ended up keeping most of the friends, partly because I'd always been the one to call them and arrange to meet etc., but partly because they were pretty disgusted with his behaviour.
In your case, I suppose the reason that they might be attempting to support him as well is because you've left him, so he's seen as the injured party, because they have no real idea of what your life with him has been like. He's probably playing the hurt and bewildered card at them - in their shoes, how would you react? So they're sitting on the fence until they have some more concrete evidence of the real cause of the break up, I'd say.
In the end, I agree that you probably should let it lie with them for a while, because I wouldn't trust them to keep quiet about what you're doing. One of my friends, she would have to socialise with the ex because her OH was the ex's best friend from school, but she would always report back on how he was, how the OW was etc. (we had a few gleeful chats) - but I never spoke to his actual friend about him, he wouldn't participate in our little sessions.
Anyway, that's enough extrapolating from my situation which is of course markedly different from yours - except to the outside world, it probably isn't seen as being much different (apart from the lack of 3rd party in the break up of course).
Let it go for now. Let things progress, fight your battle for you and your DC, if they contact you be nice, meet if you want to, but say very little except about how much happier you are away from his nasty ways. It'll all come out in the wash, as they say, and you might end up with fewer friends but they'll be ones you know you can rely on.
and
for you. xx