We have a huge space ship at some distance from a huge black hole cluster where the region of space has a quasi-uniform gravitational field of 1G. This ship is keeping it's thrusters firing in order to stay at rest relative to the black hole cluster. And, for centuries, this ship has been at rest with the cluster, with it's inhabitants at 1G proper acceleration. An observer on this ship notices an alien space station approach from the direction of the cluster, apparently in freefall, since it is slowing down at a rate of 9.8 m/s^2, and a few years later, a small alien ship approaches from the same direction, also slowing down at 9.8 m/s^2, and it looks like the alien ship will stop and start falling toward the cluster about the time it reaches the large ship, but just as the alien ship comes to a stop, it fires its engines and stays at rest with the big ship. A short while later, a second space station in freefall approaches both ships, slowing to a stop as it reaches them, then starts falling toward the cluster. Simultaneously, in the large ship's rest frame, the first space station comes to rest several light years ahead and reverses direction to start falling toward the cluster. A short while after that, the alien ship cuts its engines off and starts falling toward the cluster. A few years later, the first space station comes flying back past the big ship, and the crew notes that it will catch up with the small ship before long. The big ship's scientist remarks to the captain, "Oh, they must be doing the twins paradox". How's this for a third observer?