Bonding/Aggression

Question
Hello!  We recently adopted two 8 month old "bonded" male guinea pig brothers, Jim and Jack, from the humane society.  They were in the same cage when we visited, and adopted them a week later.  When we first brought them home, we put them in the same large cage with no issues.  About a week later, when they were outside of the cage and playing inside a large box in their play area (we were cleaning the cage), they started fighting.  Jim tore the Jack's lip (it's been sutured). Since then, they have been living in separate cages (side by side) and have been neutered.  It's been 10 days - we take them outside while cleaning their cage, they have free roam of a large backyard (carefully watched and provide them each "shelter"; however Jim will seek out Jack (who has taken to hiding more in his igloo) and Jack will Chatter aggressively. It's only happened twice since surgery that they've had "access" to each other.  I switched their cages today, and Jack continues to "chatter" aggressively.  I plan on building them a C/C enclosure, but am really concerned about the behaviors.  Please advise how best to re-introduce them to the same space, when to do so, and if putting a barrier separating them in the C/C cage (I saw one set up on a C/C cage design website) is a good option or not.  I am following advise on fresh veggies/fruits, they have unlimited access to Timothy Hay and water, using Oxbow pellets, have apple wood sticks for chewing, both have igloo-type shelters, cardboard tubes and such for play/chewing.  Sorry so long, thanks for your help!

Answer
My apologies for not being able to write sooner. I have not had Internet access until now.

Most boars, even those who have grown up together, reach sexual maturity at about 6 to 8 months of age. They become territorial and aggressive, not because they're unhappy but because they are driven by hormones.

All herding animals go through this part of their lives. As long as there is no drive to breed they will get along, but as soon as the hormones kick in they instinctively start behaving this way and fighting to determine who will be the king.

There isn't anything you can do to change this. They are hard wired by nature to listen to their hormonal drives and instincts. The safest thing you can do is keep a barrier between them. They'll be fine even if they can see one another and touch noses. But put together they will continue to fight until one or both of them are seriously injured.