Flattern curves for (region) union and then rebranch the curves again

Hello altogether,

I really would like to know how to rebranch the union objects after flattern them according to the left list. So my rebranched list should have the "closed planar curves" three time for each circles that are a union curve now and the last circular curve should get rebranched according to its circle branch in the left list. 

I actually just want to union all circles to one union object, so even when the circles not intersecting I just want one closed curve for all circles in the right list.

But some of them are not intersecting so I tried to "unflatten" the union for each branch without success....

Every help is much appreciated.