Hello again and thank you for that detailed description. I managed to make it all work quite well thanks to your input. I couldn't work with a master timeline but had to add all timelines to an array and then animate them when scrubbing back and forth.
I don't know if it's a bug, but if a sub timeline is added to a master timeline with a delay, then once I scrub past it's start frame and back (before the sub timeline's first frame) again, position, scale, and rotation is overwritten with a transform translate resetting my initial values. I fixed by adding a "key frame" on frame 0 setting all my start values. I don't know if that makes any sense (and if it's by design?).
In any case it works now and that's great
Thanx again.