[esle9]

For swallows, the forked tail is a field mark for Barn Swallow, but tail shape isn't as helpful for the others. Also Barn has cinnamon underparts and a reddish throat.
Violet-green can be separated in flight by the white patches on the sides of its rump, and the white wrapping around the eye. If you see the violet and green markings, that is helpful too.
Tree is blue above, and doesn't have the white patches on the flanks or around the eye.
Cliff has a reddish throat, light rump, and white forehead.