Each part that you want to be effected by BodyVelocity need BodyVelocity under them. So, unfortunately, you have to create one for each unless there's some other method that I'm not aware of.
EDIT:
I saw the comment to your question which said to weld all the parts. That's a pretty good idea if you want parts to move in unison and at the same relative distance to each other, but if you want the parts to move towards each other or affect the relative distance between each other, then welding would cause a problem.