> At what point do they start breaking up into unrelated orbits?
I can't speak with any authority, but in general a train of satellites would likely be moving in an orbit with either the apogee/perigee similar to the target orbits, but the other end of the orbit being higher or lower. Each time the train reaches the extremum at the target altitude, one of the satellites thrusts to adjust the other side of its orbit to target, which pushes it out of the pack.
The specifics may be so different as to make that explanation totally wrong but it's probably not too far from the general principle.
I can't speak with any authority, but in general a train of satellites would likely be moving in an orbit with either the apogee/perigee similar to the target orbits, but the other end of the orbit being higher or lower. Each time the train reaches the extremum at the target altitude, one of the satellites thrusts to adjust the other side of its orbit to target, which pushes it out of the pack.
The specifics may be so different as to make that explanation totally wrong but it's probably not too far from the general principle.