Mites and illness can cause grumpy behaviour so ensure your Guinea Pig is healthy before worrying about behaviour problems. Loads of space, as much as you can spare.
Two of everything - including food bowls, water bottles.
Food in separate areas of the cage at feeding time.
Remove hiding places and houses, cage can look boring but you are removing items they could be territorial about.Thats the key issue.
Try not to move them around too much, moving from cage to pen and cuddles can evoke squabbles.If they are going through an upset then keep movement and cuddles to a minimum.
Bathing can often help, but make sure you use the same shampoo for both pigs !!
If you have sows, try and keep them a distance from the boars if you think it may be this that is causing the problem - if the sows are in a completely different area, try and handle the boars first before the girls as the smell of sows on hands, clothes, items or faces can set them off too.
Hay is often a good distractor as well.
If they are still squabbling and looking like they are really getting on each other's nerves, try a trial separation with a mesh divider - quite often an hours "time out" can really help them calm down, but try not to leave it too long before you try them together again. Of course, sometimes they may just not be able to get along and simply don't like each other !
Sadly, there is little that can be done about this, and if they look constantly stressed even if they are not seriously fighting you will need to consider separation and alternative companions.
FACT The vast majority of boar pairs dont have any issues and stay together through teenage tantrums.
All single boars under 15mths have behaviour assessment on arrival,to help us make the right decision for them.