What shall i do-my guinea pigs are fighting?

no blood has been drawn but they have been chattering their teeth and being aggressive. they are both males and one is older (5 years) the other (and his brother who isn't fighting) are 3 months. i have seperated them in differant hutches so they can see each other but cant fight, and in their run i have put mesh accross the middle so they are seperate. also, i have bathed them all with pet shampoo so they smell the same, but it didnt work. what shall i do? i dont want them to be seperate for ever, especialy because the older one's brother died (thats why i got the babies)