I can't offer an explanation for the eyes squinting, other than to agree that it is likely they are stressed from fighting/not being able to get away from the other.
I would like to share something I found with my two though, about the blood and the perceived lack of injury.
Branston and Pickle get on fine most of the time, but occasionally one of them decides he's frisky, and chases/mounts/dominates the other
relentlessly for a few hours. It stresses them both out for a small while, then they go back to being best of friends.
Usually we don't intervene unless they are really about to get stressed (and by intervene I mean seperate them), but on two occasions I've had to do so - because Pickle got so fed up with being chased that he bit Branston on the nose.
It was unusual for a couple of reasons - firstly, there was loads of blood, probably because those incisors are so sharp; secondly, because within about ten minutes you wouldn't be able to tell there had been a bite.
Before I'd had chance to wipe the blood off/stem the bleeding, Branston had completely cleaned himself of any blood, and the cut was nowhere to be seen.
I believe that, like some other prey animals, guinea pigs have amongst their defence armoury an extra coagulant or clotting saliva, which enables them to hide injury from predators.
Basically, he's cleaned himself and licked the cut, and it's sealed and closed very quickly, and combined with his hair, it's now invisible.
So if you have come home to find a piggy that has blood where he's been sat, and either no blood on him or no injury, it could well be that he's taken care of it himself.
Sorry for the long post, just my thoughts on the subject. Hope your pigwigs get well soon, and can stop scrapping
