this guy is good...I never studied much the midpoint (I think he is referring to the Midheaven or 10th house in natal chart) didn't seem too important in relationships but it is considered a focal point...usually of a career or business context...the composite chart is the comparison of two different charts...I think that's what he meant.
all true...interesting sidenote is the thing about monogamy...some birds do better than humans.... :)
Another thing that is interesting is that Trump has a majority of planetary influences in his 4th quadrant (I guess you could say) I believe his Sun sign and quite a few others are in his 10th house...it is an unusual chart...I probably have never seen one like his.