Nothing wrong with the hay being on the ground. I personally don’t use any kind of hay rack or holder and instead only ever give hay in loose piles on the floor. I find hay racks restricts them too much and my boys much prefer to get into and lay amongst big loose piles of hay while eating.
It’s just something you need to be aware of. Most boar trios will fail particularly as you are dealing with teenagers at classic hormone spike time.
If you’ve separated one of them out now, then he may not be accepted back at all. A separation can do damage to a bond, particularly one which is as unstable as a boar trio can be, so don’t just reintroduce him to them. If your longer term plan is that they live in pairs, then as you have separated, now might be a good time to bring that plan forward.
I personally don’t use Oxbow pellets so cannot recommend them from personal experience. The ingredients look ok though. Whatever pellets you feed, ensure they are kept strictly to just one tablespoon per pig per day and never left with constant access to them.
Most vets in the UK do not recommend routinely supplementing of vitamins. It seems to be something we hear of a lot from our US members though but we do not recommend it.
He does need to see a vet for that wound though, whatever its cause, it needs to be checked over