Bisect interface between overlapped particles

Hello, I’m looking for the way to bisect interface between overlapped particles.

Please check this image.

Currently, I’ve been using the left one because I don’t know how to do in a right method.

Are there any ways to bisect overlapped particles?

If I just use ‘union’ feature, then I cannot differentiate which one is included for A or B.

I would like to bisect the interface between overlapped particles & assign domains separately.