Can you tell us how long you have had them?
If piggies are moved to a new environment they go into a period of reestablishing their relationship. During that time it is normal to see an increase in dominance but it should settle as they have reaffirmed their bond, although a certain amount of dominance goes on throughout their whole lives. You cannot limit this.
However if it has been longer than two weeks and the intensity of the behaviour is beyond normal dominance it has possibly tipped into bullying. That means their bond is not a happy one and they are likely to need to be permanently separated. Even if they were bonded at the place you got them from, moving them to a new home to bring any issues they already had to the fore and cause a bond to fail. Plus in a private rehoming, not everybody is honest about their reasons for rehoming.
Relentless and constant chasing, rumbling etc can be a sign of bullying. The underpig can become withdrawn, lose weight (so increasing the routine weekly weight check and instead weigh daily to monitor hay intake) , and have had enough of being subjected to such behaviours.
In a dysfunctional bond, squeezing through the divider, being at the divider etc does not mean they want to be together - it can in fact be totally the opposite and is just a desire to mark territory and be able to get back to the other pig to continue the bullying behaviour.
You should separate them temporarily for a few days so you can assess Tribble’s behaviour. If he perks up and is happier when Peter Parker can’t get to him, then that is a sure sign their bond isn’t a happy one and the separation would sadly need to be made permanent.
You can try a completely neutral territory reintroduction after a few days if you aren’t sure of the situation. It will usually become obvious quite quickly if Tribble was happier to be apart from him.
You do not go by Peter Parker’s behaviour - if he is indeed doing the bullying then he is going to be upset by a separation because he is no longer able to carry out bullying.
Do note that if they do need to be permanently separated, a 2x5 cage split in half isn’t big enough for each piggy. Each piggy would need a cage of a 2x3 minimum.
Bonds In Trouble
Dominance Behaviours In Guinea Pigs