Interesting that you brought that up. The other day, while trying to get in some science fiction writing, I was wondering if two Earth-like worlds could share orbits like Saturn’s co-orbital moons do.

They really don’t share the exact orbit. In the case of Saturn’s moons, one moon is slightly closer to Saturn than the other. Consequently, the closer moon orbits a little faster than the farther one. As the closer moon catches up with the farther one and interesting thing happens- they switch orbits and repeat the process.

I think what happens is that they start to orbit each other and in doing so they change orbits around Saturn.

Could this happen on a larger scale with two Earth-like planets orbiting a star.

I also liked you comment about a moon of a moon. In a story I wrote years ago, I had an asteroid orbiting a large moon of a gas giant planet.