I agree with the others. Ball fighting and loud squeaking are not good signs and if this was to happen when you were out, you could have come home to a bloodbath, so definately keep them on their own now. It`s really sad when this happens because I had the same thing happen with two male Roborovskis a few years ago and I really loved watching them sleeping in their wheel and playing, until one decided to start chasing and biting the others rear end causing scabbing. I then witnessed this bullying and had no choice but to seperate them.
In the wild, they would be able to run away from these attacks, but in a caged captivity, they can`t, so we have to be very vigilant of changes in behaviour on a daily basis for any signs of aggression or fall outs.
I`m sure your hamsters will do fine on their own and adapt well.
