Hello and welcome. The cages look good but they are unfortunately all too small. A boar pair needs a 2x5. A singleton needs a 2x3 as minimum. Is it possible for you to extend the cages somehow? Is that the door in front of the widest part of the cage? How about extending the length and going round a corner if there is space?
The alternative could be for you to stack the cages. You could have the pair in a 2x6 and then the two singles side by side in a 2x3 each - either above or below the pair.
I’m sorry your boar pair didn’t take to each other. It can be difficult (but not impossible) to bond a boar in their teens. Living as neighbours is the next best thing to sharing living quarters with another piggy. They can still have the interaction they need through the divider.
I don’t know if your title is a hint at what you are considering, but please don’t. Trying to bond one of the singles with your pair could result in three singles, as worst case scenario.
I hope you can find a way to extend the cages as they really do need that space. How old are the bonded pair?
PS your bonded pair should ideally have two hides with two exits and water bottles. I know that there’s the corner house and tunnel but I would say that’s not quite enough. It’s better to eliminate any chances of issues or piggy backed into a corner by having houses with two exits. This is more the case for boars than sows.
I would also remove the corn? chew/treat thing in the pairs’ cage. It’s not safe for them as far as I’m aware.