There are many reasons for barbering, sometimes it can be because of dominance, or just a social behaviour.
Other times if they are eating their own hair, it can be due to stress, pain or because they have parasites.
The guide below explains barbering.
If you can determine which one is happening in your case it may help you.
If there is a big dominance issue to the point that the two piggies do not get on, then do not attempt a reintroduction and don’t let them have floor time together.
Barbering ( Eating Hair)
You cannot bond them closer - they either get on or they don’t - and they certainly won’t be bonded any closer if they are continually put together but then separate each day.
If you put piggies together they start to try to form a hierarchy and bond. To be fully bonded and have the hierarchy set completely takes two weeks of permanently living together. If you put them together for a few hours floor time, then separate them after those few hours, then the whole thing is interrupted, stops and they are not bonded. When you try to put them together again for another few hours, they have to start right from the beginning in trying to form that hierarchy. Again if you separate again then it’s all undone and they never get far enough into the process to even start to form a bond. They need to be put together for a few hours, then moved into the cage and left together and they go into the two week period of fully bonding. After that and if things are still ok (ie no fights), then the bond is complete.
There can only be one dominant piggy. If they both try to be dominant the bond will fail.
Bonding is a one time thing, seen through to conclusion on one day with no further separation.
You put them on neutral territory for a few hours and if all goes well, then you move them to the cage together straight away that day and leave them together permanently.
If things fail, then they can never be in the same cage and they cannot have floor time together.
Bonding and Interaction: Illustrated social behaviours and bonding dynamics