possessives - his and her thing or things?

This might be a duplicate, so kindly excuse me if it turns out to be the case.

Do we say "This is his and her height" ? To me it sounds correct, but since we are talking about two separate heights, does my quoted phrase imply that it is both heights added together? (Nobody ever says that, i know)

For example if I say "His and her lexicon" does it mean the accumulated lexicon of Him + Her or is it treated as a separate one for each? Would you ever under any circumstance say "His and her lexicons?"

Perhaps "His and hers lexicon"?

Also, should I tag this under "grammar" or "grammaticality"?

Thank you!

Answer

"This is his and her height" would only be correct if they had the same height (i.e. 1 height).
In the same way you would not say "this is his and her name" unless they had the same name.

You could makes it "these are his and her heights" (these agreeing with the plural heights).

Or "this is a record of his and her height" or "this is a record of his and her heights" (in either case the 'this' refers to the singular record), since the "this" you are referring to is probably a thing, a piece of paper or a computer file, where the heights are recorded.