Ya, if you want to use ease then use this.ratio instead of progress. It will give you actual value that is being used to apply ease, it can go beyond 1 on certain eases. To get individual progress, use a loop to create tween for each orb.
Additionally, now that I rethink your goal, it is a bit too complex. It would be easy to create this effect by manually calculating position of orbs and rotating them around. If you still want to use MotionPath and ease then you may have to use getPositionOnPath and use these values to calculate scale, this way scale won't be tied to progress.