Yeah they will be fine hearing each other. I have two single boars, they used to be in a pair but now hate each other. I have them caged next to each other, they can touch noses through the bars and talk to each other; they are fine with that arrangement. Even as a lone Guinea pig I feel that they need to at least hear the presence of other Guinea pigs. I had Jeffrey one of my lone boars, unable to touch the other boar through the cage and he was shouting loads. The other piggy Fudge was shouting back lol So they love each other when not in the same cage, but in the same cage it gets all fired up, silly boys.