Can you help to identify these frames, bikes or parts?

Internal. Then reference standard seat post sizes for given tubesets.

A caliper would be the best choice for measuring if you don't have a suitable seatpost or seat post measuring seat (stepped-width seat post).

The seatpost that was in the frame is marked 27.0, and it's pretty snug so I assume that's what the tubing is.

Had a quick look on Sheldon but will look again later.

Closing in on this!