For Falcon's Special Power:

GOT YOUR 6!: Give Falcon a free action and choose one: Empower, Enhancement, or Sidestep. Falcon and friendly characters named Captain America adjacent when this action begins can use the chosen power until your next turn.

Can this be used for the Captain America and Black Widow Duo? Or do I need to wait until they are split to affect the Captain America 'half'?

No. "characters named Captain America" is a specific name so it must be just "Captain America." If a power specifies a name, it needs to be that name... there's a couple powers that say if a "friendly character named Iron Man..." and they don't work with Iron Man Mark ___ because it's not "Iron Man."

On the flip side, First Lantern has a power/trait that says if they have a keyword that CONTAINS the word, "Lantern"... that's the other side of this coin.

Eh, I figured as much. Still though, can't wait to play the team! Thanks for the assist!

Yellow Lantern approves of this message.