Hi BR - welcome back
It does sound like you have your hands awfully full, and potentially more than you can comfortably cope with right now.
I think Gill has made some very pertinent observations, and it is generally helpful to try and break things down into bite sized chunks when trying to work out where the solutions lie.
If you turn this around, and look at things from the viewpoint of the cats, they've all gone through an incredible amount of change in a relatively short time. Whereas, we humans can talk about how we feel, and have the ability to turn to our friends and Purrs family for support when we need it, our cats have no such opportunities. and sometimes, because of that, it seems to us their behaviour is out of control, or that as Gill mentioned, we feel they're doing it on purpose or to "punish" us in some way.
When cats toilet inappropriately, it can be down to a medical issue. However, a lot of inappropriate toiletting is down to stress, pure and simple. There doesn't have to be fisticuffs and fur flying for that to be an indicator - the peeing is what the cats are using to try and map out "their" territory and "their" people. I imagine there are other signs the cats are stressed, but it's not always easy to read them, especially if you're under the cosh yourself.
There was a Horizon documentary on TV last year which showed a woman who had a household of around 7 cats, all of whom, on the face of it, rubbed along well.
It wasn't until they put camcorders on their collars that they discovered one of the cats was being mercilessly hounded by one of the other cats, to the point where he befriended an elderly man up the road, and would spend as much time as he could there,. His owner was blissfully unaware, and thought everything was fine until she was shown the footage.
Your cats have moved home. They have new companions (whether or not they wanted them), they have the bustle of a small child. They have to share their space with increasing competition. Another child is on the way. Their humans are stressed. They get shouted at. They just want their world to be "normal."
Shouting, disciplining and yelling at cats doesn't work. They don't function like dogs or children. I'm not surprised Archie peed, really. He's desperately trying to tell you that he's miserable. He's wanting to keep you, your OH and his little boy as "special" and "his" and if he is less secure than the other cats it's vital that he gets the resolution he needs.
There was a recent Jackson Galaxy repeat of a family who lived in a large, beautifully furnished home, which their cat was slowly destroying. The Father couldn't contain his rage and was yelling all of the time that the cat had to go - they'd had to put a tarpaulin over the bed because the peeing was so bad. They'd had him 9 years, and yet he was now totally out of control.
It became apparent that they had two toddler aged children, who were not naughty kids - just loud and boisterous. They had a new born infant. The Mother in law (and her cat) had moved in to help the harassed Mum out with the kids. Everyone got along great. Except for the cat, who was basically traumatised by the noise, the additions to the household and the ways in which his life had changed.
If your cats are indoor only cats, the pressure on them all for a territory of their own will be phenomenal.
One of the solutions which helped to ease the situation to a manageable level in the Jackson Galaxy slot was giving the cat greater access to all areas of the house, and to provide a whole lot more litter trays in the favourite peeing spots - even on the bed, unpalatable though it sounds. They were eventually able to take them away.
Safe places for the cats to access - ie some high up spots, and plenty of cat platforms - can help if you have space for them.
You could try feeding the cats in different places. Your OH could help with that - you could feed two cats in the kitchen, on their own, and another two perhaps in one of the bedrooms, and another two elsewhere - or a three and a three. You need to work out the dynamics of your cats' relationships to see what would gel. Usually cats in a multi cat household will bond with another cat or cats, or there may be one who just prefers to be alone - in which case they could be the one that gets fed separately.
It's hard when you have a small child, and another on the way. Most Mums are pretty harassed in the early years. To then find yourselves with more cats than you'd bargained for....
Having said that, hundreds of babies and children grow up with cats and come to no harm, so there maybe an element of managing your own fears and expectations here as well.
How did you come to have Link and Zelda "dumped" on you? It sounds like it wasnt something you would have sought out voluntarily, and therefore I wonder if there isn't some unconscious level of resentment or frustration at finding yourself - however motivated by kindness - with two more members of your household that have unbalanced the existing mix. What was the relationship like with your existing 4, before Link and Zelda came?
I cant help thinking that most of what's going on is actually falling to you to put right. I think you're under pressure from all sides, and that to a degree you feel caught in the middle when you're trying your utmost to make things work.
I can understand why you may not want to part with any of the cats, but realistically, if you have too much on your plate to cope with, it may be the only way you can have peace of mind, and the cats can have a chance at a situation which works for them.
Gill made a very good point - you need to write a character reference for your cats. Consider how they interact with each other and with you, your OH and your son. If you have to make a decision to let one or more of them go to a rescue for re-homing, then it may help you choose which cats would benefit from remaining, and which would benefit most from being rehomed.
I cant imagine having to face such a heartbreaking decision, but all of us have to manage what's happening in our lives the best way we can, and there would be no shame if you had to relinquish two or more of the cats, having given it your best shot.