Congrats on the new dog.
But I don't see why you should get a trainer to make the dogs like eachother :?
I think the best thing is just to leave them alone.
I had 2 cats for a couple of years, and then we got a dog. At first they were a bit scared, but after a while they even started playing with eachother. (A lot of fun to see a dog and 2 cats play together)
I bet it'll be the same for your two dogs.
It could take some time, be patient