There seems no way, to save smart prop with all child prop.
If you hope to keep each handles as separate obj (prop)
you may need to save them as individual smart prop, one by one
with keeping each hieralchy. (the item which you hope to save, and the parent item )
1 save the watch body as smart prop parented Actor, you seems have done it.
2 save each parts as smart prop one by one parented the body part.
3 when load them, you may need to load each item one by one with selecting each parent.
Then it work as I expected.(sorry ,, too foolsh pic,,I think,, ^^;)
load gen, poze him, select gen.
then load base. next select base. load each watch handes,,
they can keep their hieralchy, and translation (scale too) as one watch.
or you can save watch (your watch bas and watch hands) as scene subset
to keep each postion and hieralchy as one subsets.
but you may need to adjust position when you load watch for your actor.
It can not auto parent .
I tested them with wealable preest, but it can not work about prop, as we expected.
(can not be smart prop, I think)
Click thumbnail to see full-size image