Congratulations! If you can have your doggies meet your potential new family first, that would be ideal. If not, ask the breeder to describe the new dog's personality.
When I brought my second boy, the boys got along great, but we had some jealousy issues to work out with Max (who is very dominant
). We put Max first for everything to reassure him that he is still number one.
Everything depends on the individual dogs. Some will work beautifully together instantly, others will take time to sort things out. It's just a matter of being observant and knowing when to stand back and when to step in.