Number of Pets: 3
Pet Type: Dogs
Pet Breed: Beagles
To: United States
Last year, we moved to Germany from US and had all the required paperwork.
1. What do I need in terms of paperwork to return TO the United States?
2. Can I get a “passport” so the dogs can travel between Europe and the US multiple times during the year?
As a seasoned traveler it sounds like you're in pretty good shape. What you'll primarily need to focus on at this point are the pet import requirements for the United States, which fortunately aren't overly strict, and if you go back to Germany, the pet import requirements for Germany.
Traveling between the US and Germany isn't quite the same as traveling within the EU, so you will need to obtain a health certificate each time you travel (this is issued by your vet within 10 days of departure). Please take a look at these links and then let us know if you have further questions or if you'd like assistance.
Good luck with your travels!