FussA, interesting what you said about mild ASD, because that's going through my mind too.
I think it's possible to have one or more ASD traits without being full on ASD as well, though the professionals seem to prefer either/or diagnoses.
You can't make a diagnosis from a forum post and no-one would seriously try - but a little boy who seems to be a control freak with social skills problems is not necessarily, solely, reacting to home life. It's a question of how the control thing comes out, and the social skills.
For ASD I'd expect to see a little obsessiveness about order and how things are done, and temper if it doesn't happen as predicted. Social skills ? things like not realising what is appropriate in certain situations, or not having much empathy with others.
For the little girl, I've seen a pattern like this ?demanding at home, quite controlling, but hard-working at school and (this is key) very keen to look good in public. Only an observation though.
With the DH?something out of the ordinary there. He's acting more like one of your children, OP, than a partner.
With the bath/washing basket incident, instead of joining you in (preferably gently) disciplining your child, he calls you a filthy name in front of her and throws a tantrum. Says you ruined his day by missing the awards ceremony? Now I'm presuming he didn't say 'Darling, I DO want to see the awards ceremony, let's go back' but assumed you would remember? Then got upset because you didn't?
This isn't really normal behaviour for an adult man. Even if you heard and dismissed him (and you didn't, apparently), a typical adult man would, frankly, remind you and assert himself calmly at the time.
Similarly the water incident ? a good parent would say 'that was rude, I don't want to hear that again' and offer a consequence if appropriate. And both parents would agree on that. Water in the face?? That's a child having a tantrum again - and abusive. A very unhealthy parenting environment for real children.
It's rather worrying that he doesn't take responsibility for his anger either.
For you brake, nothing to add here except that I recognise the 'I don't do lego' thing from my own childhood. It was not a problem. The overall experience is what matters.
Sorry that was long, and I am not contradicting what others have said, but trying to offer a few other thoughts.