Hey! So me & my girlfriend rescued a guinea pig last year from a local SPCA. (His name is Felix). He was only 2 months old, and about a month after getting him we decided to get another. So we got Hammy, a 3 month old. We followed every step to introduce them, and only after a couple of days of figuring out their dominance, they were living together and have lived together in perfect harmony ever since. They decided Felix was the more dominant one, they loved each other but if any small (but almost playful) incident happened it was because of Felix. The worst it would get is just them chasing each other or growling (but not chattering teeth) for about 5 seconds then they'd move on. We thought of it as just brotherly love. They never bit each other, never got actually aggressive. It's been less than a year since we've had them, and every second has been perfect. So, we decided one more would complete our little family! We got a 3 month old named Blue. We knew it would be different because Hammy and Felix have A) bonded and known each other for so long and B) Blue is younger than them. So, we put them in a neutral space that has everything each of them need, and it was wonderful! Mild growling, a little bit of that butt sway thing, and Felix tried to mount him one or two times but only for a second. So we decided that was enough for a little while and put Hammy and Felix back in their own cage. Felix went CRAZY and started biting Hammy and ripped some of Hammy's hair out! they were full on brawling, teeth loudly chattering and they were like rolling in a ball fighting. So we separated them and now that they are in separate cages, Felix is biting onto the cage and shaking it so aggressively. I don't know what to do because i don't understand how they can live peacefully for so long but suddenly Felix is legitimately attacking Hammy. Meanwhile, Hammy and Blue are fine together, no aggression, they just go back and fourth trying to mount each other, which we think they just both are trying to show dominance, but not aggression. What do we do?