I find that this could fall under the category of "I want all destinations with flags that contain blue but don't have stripes".
Finding a public service that can do this is hard but that doesn't stop you from developing an app of your own that can do this.
There are a lot of Flight API's available and combining these with some geographic data (idk what ...
Google Flights allows one to search for flights on a map. You could enter "Spain" or "Europe" as destinations.
Having the results on a map allow for easy exclusion simply by only looking at areas of interest.
While not a perfect answer this is easier than looking at a plain list of flights to mixed locations.
Since the last passenger arrives at terminal 2A the best thing to do would be to meet everyone at terminal 2A. What I would do is:
Friend 1 stays at terminal 2A arrivals in the area outside of baggage claim
Friend 2 transfers from terminal 2E to 2A arrivals; this takes ten minutes on foot
Friend 3 arrives at terminal 2A and finds the other two friends ...
I don't know of a site that does what you want but using Kayak Explore (https://www.kayak.com/explore/) you can see a map with the prices displayed for a given date and can help you get out of the region for the lowest price
The US cannot refuse entry to a US Citizen, which of course you can prove you are by showing your certificate. That being said, they will likely have to verify it and that may take some time.
The US Dept. of State says:
If you are a U.S. citizen crossing into the United States from Mexico by land without a U.S. passport, you may be slowing down the ...