I don't agree with this. My two are together all the time. Chewy is almost 2 and Sadie is 19 weeks. It would be horrible to keep them apart. They are buddies.
I would think who ever was going to be alfa would be. We thought our puppy SAdie was going to take charge at first. (She tried to) But after a few days chewy took over and decided he was top dog. I guess we will see...I was told the girls like to take charge!