Oh boy, how many of us have been in Diana's shoes?
"I have two male guinea pigs...father and son and they have lived together since the son was born. Kiko (the father) is around 2 years old while Ringo (the son) isn't one yet. They have lived together with no problems. Lately they have become very strange, chattering their teeth at one another. Ringo chases Kiko around the cage and throws himself at Kiko. Kiko...has become very scared and hides wherever he can. He has been tired and sleepy most of the time, while before he was very active and generally good humoured. I'm not sure whats going on. I've separated them because I'm scared that when I'm not there something bad will happen and I can't help them."
Diana did the right thing by separating her boys. Ringo is relentless and Kiko is miserable and showing signs of depression (i.e., hiding, lethargy). But what happened?
One word: Hormones
After months of being a dutiful young son learning from his dad how to be a big boy, Ringo is individuating from his father. His hormones are surging and he's thinking he'd like to be alpha male now -- and he's basically wrestling with his father to claim that title. Although the seemingly gentle-natured Kiko apparently isn't putting up a fight, Ringo seems determined to keep hammering on this point. He's behaving like a bully now, and Kiko is clearly feeling victimized.
You can keep them separated for a short time and try reintroducing them a little later. Maybe they'll restore harmony, maybe you'll see the pattern repeat. (I suspect the latter will prove true. If you do end up having to permanently separate them, keeping them in side-by-side cages or side-by-side partitioned areas in a very large C&C cage should give both pigs enough company and socialization to keep them from getting lonely or depressed.