Oh my! I'm excited for you!
May be best to introduce them to each other outside the house, on a walk. Then, when inside, give them both equal attention.
If Jax seems depressed at times... do give him extra attention. I'm juggling 4, and one of my girls got a little down at one point. I just made sure to spend special, one on one time with her, till I could see she knew I still really love her too, and now she's fine.
I don't play favorites, they are all my favorite. I have my fav old, boy dog, my fav little girl, my fav big girl, and my fav middle girl! So each is special in my eyes in their own way. Or, to put it another way... I found a reason to make each one feel special, silly as it may seem... they can tell if you actions don't match what's in your heart.
Waiting for tons of pics!
Or Jemma?