I have two, at first we didn't always let them near each other, as the older one, Yoda (who was almost four at the time) wasn't too fond of Winky, the baby, yet. As they got used to each other, we did let them stay together more and more, and that worked out fine. It was mainly Winky trying to "bug" or nip at Yoda, as Yoda was quite good about it, and didn't try to attack back or hurt the baby. I think mainly it takes a bit of time before they get used to one another.
