I had the same situation when I went from two borzois to 3. The pup came in full of himself and being a show dog, we had to encourage him alot. Yea well- about two weeks into this, femka instead of playing with him like she was doing, started getting nasty with him. Because he was a puppy, we were trying to protect him.. and it got worse! Finally I called the rescue where we got her from thinking her past was the problem when she dropped a bomb shell. By us not scolding the puppy, the adult ( Femka) was like " I will get him better next time: and it became a down spiral.
We reversed tactics. When they would play and she went to snap at his face, we told zubin "NO" saying nothing positive to Femka but not scolding either.. This whole thing stopped in two days! And now they are buddies. Zubin knows she is boss over him and he doesnt challenage her because of us but she thinks she won.
Fuss at the subdominant- the last one in the house. As I say " No- wellllll no.. whats the matter with you Zubin..." and its peace in the family..