My mum is a bit like your dad. And my dad enables it by having never addressed it, like your mum does.
My mum can be very supportive but then has times of being very stroppy and self indulgent. And sulks. She'll kick off about something and when she knows she's been unreasonable she will sulk. When I was a kid the sulking could go on for days and we'd be in eggshells, my dad would be grovelling round her and after a couple of days she'd flip back to normal. In reality whilst she may have had reason to be a bit irritated about whatever triggered it her reaction was something she should have been asking forgiveness for but no, we'd all be made to feel we had been unreasonable. It was a weird cycle and she continued to do it until a few years ago with me (I've not lived with them for 20 years so this would be by sulky text or ignoring mine of my calls). I make her sound hideous but these incidents weren't that frequent in fairness but were hard going when they happened.
A few years ago we turned a corner - we had an argument in which she was completely unreasonable. I was dealing with some pretty awful stuff which she had been really supportive about and something triggered one of these episodes. I simply refused to do my usual 'leave it a while then get in touch like nothing is wrong and be overly friendly so as to make the peace'. It ended with her contacting me, eventually - weeks later! And me standing firm saying I was hurt by how she'd made me feel at such a difficult time. I made it gently clear I couldn't move on without an apology or acknowledgement. Which I got. She's never been good at apologising and I think the difficulty of her having to do that was enough to change her behaviour with me and we've never had such an incident since.
So my advice is to stick at what you're doing, I know if I'd emailed my mum explaining these traits it would not have been well received. And wouldn't have resolved the situation. But then I wouldn't like to get correspondence which highlights all my flaws. Eventually if he comes to you, even not to address the situation, but to try and move past it by contacting you about something else, consider what your response will be then. Either go with the flow and see if he had learned not to behave that way with you again because of the consequences of last time or address it politely head on that you are still hurt by what happened before and request an apology.
It's a form of domestic abuse, which isn't solely down to partner relationships. The telling thing about such abuse is that people only do it with their families. My mum doesn't silk for days at work (I assume!) So it's a conscious decision to be that way with family. Therefore they can change and make the conscious decision not to be that way. It's just about finding the right way to address it with that person I think.
Sorry have rambled on forever!