I am very happy for you and your decission to add another dog into your home and heart.
The one I expected to change a little was Hottie. Except for earlier in his life, he basically was an only dog for quite awhile- as in several years. I was prepared- told myself the new comer would not know if I was adding more attention to the "the boss dog" ( Hottie) but HOttie would know if I started giving him less attention. To my shock, not only Hottie get along fine with Femka- but I also saw a change in Hottie that was for the good. He started to play more, seemed to enjoy more walking in a "pack" out in the yard, and quickly became buddies- while maintaining being such as sweet with us.
Hotties medical condition, he needs to exercise more, but without stress. To see them play, he is obviously under no stress. I even feel that having the other dogs has helped him quite a bit be more active- build stronger muscles, and less of a " throw rug" in the house except for daily long walks.
When Zubin came, I expected a little jeolously from Femka. Not only did that not happen but Femka turned into a puppy with Zubin. And when Galina came, Zubin had gotten bigger by then, and with Galina being shy- Zubins antics pulled her out of her shadow as a wall flower to a silly brazen hussy, and wonderful show dog.
Take it for what its worth- but I can see like ages, like in breed, play alike. Hottie plays more with Femka, and Zubin and Galina play with each other. I can see Femka wants to play more, but Major will fix that one. He is much smaller than the two pups, and being a neutered male, no challenage to any of the others as well.