That won't work because the on drop event already narrows it to one instance of family, you have to find some other way. Using the specific object type on drop to check if it is overlapping family would work, pick by UID condition also wouldn't be necessary.
So you would split out events into object A on drop, is overlapping family. Object B on drop, is overlapping family etc. Could be a few events with many draggable objects but it seems like the only way.