Your piggies are now at the start of their teens and seeing an increase in dominance is to be expected.
You must be very careful not to confuse normal dominance with aggression - rumbling, mounting, chasing, mild teeth chattering are normal and you do not step in for those behaviours.
A full on fight or if it looks like it is leading to one, is different. If that occurs then it Is sadly bond breaking and will require permanent separation.
With teen boars it’s generally the case that you leave them to sort things out between them while it is just mild dominance.
You can carry out a temporary separation for a few days to allow hormones to settle down if things get a little too heated. You can then, after a few days, reintroduce them on neutral territory (don’t just put one piggy into the other piggy’s cage as it may be seen as a territory invasion) so they can decide whether they still like each other and wish to still be together. What you can’t do is repeatedly separate and them reintroduce them.
Its important with boar pairs to ensure that you have a large cage - measuring 180x60cm or a 5x2 c&c on a single level (upper levels don’t count towards the cage size). Anything less is likely to be too small and lack of space can cause issues between boars.
Also ensure you have multiple of every item, including multiple hides. It’s also important to ensure all hides have two doors. Single exit hides can be a flashpoint and lead to fights.
The links below will help with further information
A Comprehensive Guide to Guinea Pig Boars
Boars: Teenage, Bullying, Fighting, Fall-outs And What Next?
Dominance Behaviours In Guinea Pigs
Bonds In Trouble
Bonding and Interaction: Illustrated social behaviours and bonding dynamics
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