I believe GroupActors are editor only and would not work once your project is built for shipping anyways. I think the transform tool has specific knowledge of group actors to forward the transforms onto the items in the group.
A better way to do it in Sequencer would be to actually reparent these objects under a common ‘null’ object (empty actor). This would let you animate the empty actor in Sequencer, and also animate individual parts as the Transform Tracks are applied using relative locations/rotations, so the animations would be relative to the null object.