Thanks for this very informative answer. However it only solves part of the problem, in my case.

I have a large tree of my own ancestors, plus ancestors of my wife. We now want to separate these two trees, through copying the combined tree, and then deleting one side from each copy.

The difficulty is that both sides of the tree contain not only direct ancestors and peripherals, but also descendants from sibs of the direct line, (and family of relatives by marriage). In other words, we each have multiple cousins at varying degrees of separation. The Extended Family Chart does not pick up cousins, so how can we ensure that all these additional "undesirable" people are deleted?

Thanks for any help