We are going into Week 3 of adding Jack to the family. It is getting better.
Nessie, our Aussie, has guarding issues which we handled pretty well with our older dog. But the stress of his death and a new puppy, we decided to consult a trainer before Jack came. Good thing!
Outside - things have calmed down quite a bit. They walk very nicely together. Playing is kept to a minimum because Nessie weighs 40 lbs but they do the 'wanna play' stance with each other. The only thing I am not thrilled with is that Nessie tries to block/herd Jack away from the door. "It isn't going to work, Ness. He lives here now. He has to go in."
Inside - whole different issue. Nessie showed teeth and growled big time! The trainer told us to set up the house so that they are never in the same area. A barrier between them at all times. I did mess up the first day trying to figure out traffic flow and Nessie bit Jack. minor blood, everyone was okay. (Later Jack growled back at her.
After 2 weeks, it has settled down. Nessie is still unhappy but she doesn't snarl every time she sees him. Growling happens if Jack tries to approach her area but I do see the light at the end of the tunnel. Maybe by next year, we won't have to crawl over the ex-pen all of the time. sigh..... I regret getting the taller 30" ex-pen.
Remember that most adult dogs don't care for bouncy puppies. Tolerance levels vary. My case is more extreme because Nessie has issues and they are two different breeds and sizes. Hopefully, you are blessed with a non-grumpy dog who likes everyone.