Hamsters tend to be nocturnal, if any of them is acting strange it would be the one running round in the wheel all day, if when you bought them they were already in the same cage, they will have run ins, but tend to be like squabbling teenagers, they soon get over it. if you bought them from seperate shops or cages, they can bully one another. I have 2 myself and one is hyper and the other likes to be left alone to sleep. If there is alot of sqealing, particuarly at night or you see them fighting alot i would seperate them.