Fighting When do I give up, and how do I proceed from here?

I have had my two boars for about a year and a half. I adopted them through a rescue and a rescue employee had them for almost a year prior to that. They have lived together as long as the younger boar (about two years old now) has been away from his mom. When I got them, she said they had normal dominance but generally were cool with each other. For the most part, that has been my experience as well. I often say they are like brothers: they antagonize each other, bicker, and aren't exactly cuddly but seem to happily tolerate each other.

However, in the last few months I have had a few "flying ball of fur" incidents with them. I have always separated them to make sure they are ok, and then gone through reintroductions with a buddy bath and a clean cage. They will be cool for a few weeks, and then it will happen again. There have been no major wounds, but the older (and usually more dominant) boar got a bite on his nose and I have noticed a few nips on the younger boar's ears. On the 4th, they were extra stressed out because of all the fireworks and they ended up getting into the worst tussle I have witnessed to date. The flying ball of fur lasted for several seconds before I was able to separate them. The result was a bite on the younger boar's rump (maybe about a 1/4-1/8 inch across and equally as deep) and a bite on the older boar's lip.

I currently have the younger one in a temporary grid pen so I can make sure they are healing ok and figure out what to do next. So I have a few questions:

1) am I doing something wrong in how I have been handling these altercations? I never separate unless it is a full-on ball of fur situation. I have not kept them apart for more than a few minutes unless there was a bite or unless they ended up in a ball of fur right after. In those cases, I have kept them apart for a few hours so I could clean the cage and then give them a bath and put them back in together. After this process they have always been cool for a few weeks so I didn't think it was an issue with the introduction, but maybe the clean cage is not neutral enough?

2) Should I continue this pattern, or do I need to cut my losses and separate? Separating would be kind of a pain and I would rather not end up with four pigs, but I also don't want to leave them in a situation that is dangerous or stressful.

3) If I do separate, I assume it is better to try to get them each a new buddy rather than just making them "grid friends"?

4) I have read a lot of people have had luck with a male/female pair as long as one of them is neutered/spayed. Would that be my best bet?

Note: They live in a 3'x6' one-level cage and all hides have at least two entrances (two of them are corner "fleece forests, so they are completely open. They do tend to get fed in one central location, rather than two. However, that is because when I was feeding them in separate locations, they would still both eat at the same place. They also only have one hay bin, but it is very large and can be accessed from multiple sides.