My officious quibble regarding "direct descendants" -- there is no such thing as "indirect descendants".
Is there a group noun which includes cousins, uncles, and aunts? Is an uncle or an aunt just a special case of a cousin? Then there are nephews and nieces. Is a male sibling a special case of nephew?
I've heard mention of a "direct order" in the military. Is there such a thing as an "indirect order"? Do you have to obey such a thing?
Electrical terms include "direct current". I've never heard of "indirect current". Would that be lightning?
I have a direct descendant (my daughter) who is a linguist. I may have to ask her.
Thanks, cousin.