Terrence and Phillip have their own cage or do they share a cage with the others?
Perhaps neither cares to be dominant over the other. Not every chinchilla or every pairing in every cage will have the issue of dominance.
Usually the one without the whiskers chewed is the dominant one or trying to be the dominant one, if everyone else in the cage has chewed whiskers but for them.
You'd be surprised what babies can do even at 8 weeks of age. I've heard of babies chewing mom's ears to little nubs at as young as six weeks of age. Biting or even attacking their own mother/siblings has been something mentioned in the past on occasion with babies as well (again, not a common event, but happens. Usually it is associated with not enough milk, but can be other circumstances too.).
It's not common - not at all - but it can happen.
Babies can fight over milk or lack of milk (and in some circumstances, kill their siblings due to fighting or seriously injure them.), even in the first week of their life.
Although it isn't usual with every baby, there are some babies as young as 6 or 8 weeks of age who do show dominance with the humping, the whisker chewing, or other obvious signs of dominance with siblings or their own parent(s).
Majority of babies are not like that however. But just like people, each chinchilla has their own personality and no two are exactly the same.