My (late 30) SIL's husband (late 30), let's call him Ben, is not a bad person but is quite childish in the handling of his emotions.
The positive side is that he vibes with (my) kids a lot, being the cool uncle and such. The negative side is mostly with the rest of the adults in the bunch, my in laws, my husband and myself.
We live in different cities, but it regularly pops up when we see each other. Ben especially has issues to handle his anger and worries, the most notable examples revolving around his daughters (1 & 3). If someone does something wrong with them, he comes in and starts berating. He does not raise his voice or ever hands, absolutely, but he's very tall and runs in the room asking repeatedly "what happened, what happened??" if a kid cries loudly. And then makes usually my SIL feel guilty, way longer than the situation, in my eyes, requires.
As an example, once my SIL could not find a little piece of a clock that she opened to change the battery. She searched everywhere and then thought that maybe the smaller one (6 month at the time) ingested it. When Ben found out he berated her for an hour, and still is convinced that it was insanely irresponsible. The piece was found afterwards.
On the other hand if he does something dangerous or wrong with the kids (and of course it happens) and my SIL says anything, he tells her to relax and stop being so anxious. He left the 3yo on the border of a pool without protection for example and did other stupid stuff.
He is aware and recognise he has anger management issues, so it's not pure gaslighting but he's also not getting better at it. All the rest of us find very problematic this behaviour and have spoken to him and to my SIL, but she says he's a different person when he's not around us and he feels our judgement.
My problem: I don't want to solve their marriage but we spend extended time together in the holidays. And he makes us all so uncomfortable with the way he treats my SIL and react to any comment of ours. I need a clever way to deal with this, to not be shaken to my core every time this happens. Any ideas?
TL;DR tricks to deal with my BIL childish anger management please!