Fighting Guinea Pigs Fighting.

[OreoandBrownie]

I have two guinea pigs, Oreo and Brownie. They are both males, approximately 1 years old. We took in Oreo in June from a friend, and knew that we had to get a second guinea pig. About three weeks ago we got Brownie, and introduced him to Oreo about a week after that. We introduced them in a neutral setting, and Brownie seemed excited and friendly with Oreo, but Oreo was chattering his teeth LOUDLY, his hair was sticking up, and seemed very angry. I think this scared Brownie, and we decided to keep them in separate cages and try to introduce them again later. We kept the cages next to each other and they were squeaking at each other through the cage quite a lot that night and into the next day and sort of climbing up on the bars to look at each other. The next day we decided to introduce them again, and it seemed like Oreo's temper completely changed, he was obviously displaying some dominance behavior but he wasn't chattering his teeth too much or seeming too aggressive. We let them have floor time together for probably about 2-3 hours. We cleaned out the cage oreo had been staying in, the food bowls, water bottles, pigloos, and anything else going in the cage. The cage size is 2x4. We put them both in the cage together, Brownie hid in a pile of hay while Oreo ran around smelling everything and popcorning around. We monitored them for a while to make sure they were getting along, and everything seemed fine. They even hid in the same pigloo together when I ran the vacuum. The next day I gave them both a baby carrot as a treat. Oreo must have finished his first, and I think he was trying to steal Brownies. They suddenly both started chattering their teeth very loudly, and then suddenly started fighting. I think that Brownie attacked first but I'm not sure. I immediately pulled my sleeve over my hand and reached into the cage to get them apart. Oreo was bleeding in one spot, so I took Brownie out and put him back in his original cage. I wasn't sure what to do at this point, and I was shaken up that they had fought like that. I kept them separated for a few days and they kept doing the thing I mentioned earlier where they would squeak at each other through the cage and climb up on the bars. I decided to try and put them around each other again, and not even five minutes after I took them both out they started fighting(I have no idea what caused it). I separated them quickly and anytime they see each other now, other than through the bars of the cage, they start chattering their teeth loudly. I don't know what to do because Brownie is in a smaller cage that probably isn't big enough for him to stay in for long, but I can't move them into the same cage and then them fight and one of them get seriously injured I don't know if I'm doing something wrong, or if maybe they just aren't going to get along and I need to keep them in separate cages. someone please give me some advice!