Are you talking about introducing three guinea pigs? If so, I wouldn't recommend it. Trios of boys rarely work out and may result in three loan boars. I haven't had personal experience of this but I know what boars are like and have heard people's stories, someone who knows a bit more might help soon. I would also double check they are both boys so you don't end up with babies, if you need help telling the sex you can post some pictures. When counting floor space, it's only the biggest floor that counts, rather than levels. So 10 sq. ft. would not be enough for three guinea pigs but is great for two. Can you have two different cages? Is there a way you could split that cage and have your new pair on one level and your other pig on the other level. Then you could get the lone pig another friend ( advice can be found in the behaviour and bonding section ) and have two separate pairs?