Does a player wielding whip gain advantage if it is 10 feet away from the target?

We had an episode in combat tonight that I was not sure how to adjudicate.

A player character (PC1) with a whip was 10 feet away from an enemy.

In between PC1 and the enemy was another player character (PC2) that was prone.

On the far side of the enemy was a third player character (PC3).

Does PC1 have advantage in attacking the enemy with the whip? Why or why not?

If PC2 stands, can PC1 still attack the enemy using the whip, and would this affect advantage in any way?