Let's say a figure has the sharpshooter ability and 2 targets.
When they are adjacent to an opposing figure could they target that opposing figure and a figure they are not adjacent to for an attack?
Or can they only make ranged attacks on adjacent figures when they are
base to base?

The latter. When adjacent to an opposing character, characters using the Sharpshooter ability can only target adjacent opposing characters.

From the Player's Guide:

Ok, thanks.
It came up in a match the other day and I wasn't sure.