The thing with bringing a new dog into the house is that it can take some time for them to adjust to each and learn to live in harmony. When I brought Beaker home he had already spent a week with Smudge outside of the house so got along fine with him but Winter and Tama hated him and wouldn't have anything to do with him for the first week or so. Now however Tama and Beaker are best friends and can even be kenneled together and Winter plays great with him... Perhaps the two of them just need to get used to being around each other and find a play style that suits the two of them. At work we have quite a few dogs that are in the same family play great with each other but end up being in different play rooms because of a difference in play styles.