I have a 7 year old and a 3 year old. Both of them acted up around this age. Some of it may be connected to the divorce, but a big part of it is often just the "terrible 2s". At that age they are trying to assert themselves. Divorce might be a contributing factor.
SO, the only advice I can give - pick your battles! A lot of times they do what they do to see how you'll react. If your son sees you react a certain way, he'll want to confirm that it works the same way every time and will do it again and again, especially if he know that's what gets you going. It sucks, but it's completely normal for them. Often, if he doesn't see a reaction out of you, he'll stop after trying it a few more times. So, bottom line - if what he is doing is not safe for him or the baby - that has got to stop. If it's a question of something that's not that important - let him at it for a few times and then he'll stop on his own if he doesn't get a reaction out of you.
Read up on "terrible 2s" (which, by the way, will morph into terrible 3s before too long). THere is a ton of literature and lots of good advice on how to handle 2 year olds. Most of it will probably be applicable in your situation.
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