Most of the time there isn't fighting involved if they chew whiskers or hump one another.
It is just one chin asserting themselves over the other. The reason one may hump the other is to get their scent on the other one to get them to accept them. It happens a lot with pairs. You'll notice the one who is more assertive is also the more outgoing of the two, while the one who has the whiskers chewed would be the more passive one of the pair.
Fighting is completely different. If they are fighting, there would be fur pulled, lots of kacking, chasing and possibly spraying involved. Chewed whiskers are the last thing a chin thinks about that is planning to fight or hurt the other cage mate. If a chin wants to hurt another chin, they just pull fur, chase them around, spray, or bite (usually around the head or neck area is where they go for when it comes to attacking another chin.). You can tell the difference between an accepted dominant/passive relationship between two chins and one that is an aggressive or fighting type of relationship quite easily.