I think that it's been hard on this post because the OP didn't mention any extreme behaviours, and only those who've dug through history are able to see.
That's because there aren't any extreme behaviours, except from the son.
There really isn't much more re the husband. There are lots of posts over the years about the sons behaviour, sex, porn, innapropriate images of his gf, going AWOL, drink, smoking, sulking, refusing to do anything round the house, refusing to do schoolwork, destiny, him squaring up to his dad etc.
There is a post from 4 years ago, where OP is understandably grumpy about her husband's drunken behaviour and him visiting a strip cub.
The only mentions of things 'getting physical' are (1) a mention of mum holding son by the arm at one stage (from memory to stop him jumping out of the window or something), which resulted in the son complaining to his friends that he'd been hit (2) dad pining the son in similar circumstances - the son tried to jump out of the bedroom window (3) mum posting that she was worried her angry son was going to hurt her husband or himself.
Dad isn't going to win any parent of the year awards for being shouty when his son is being lazy and rude around the house, but I've seen no evidence that he's been bullying the family for years.
Incidentally, the other son (who gets on well enough with his dad that mum thinks he might move with him if dad moves out) is having a difficult time with his MH to and lockdown, and threatened to kill himself 3 months ago. There have also been a lot of references in the past to the older son being nasty/calling the younger son names, though unsure if that goes beyond what is normal for teenage brothers. Given this done good relationship with his father and emotional fragility, I'd worry about him if the family split because of the older brother. I think it might also dive a huge wedge between them - older son acts like a brat and mum leaves their father to sit him, even though this will make the other son, who doesn't behave like this, and has been recently suicidal, suffer and choose between his parents. It's a horrendous idea.
This family needs some urgent counselling to get to the bottom of what's going on.