So when it comes to Ancestor worship, who exactly counts? Does it have to be someone you're a direct descendant of (this would be the most immediate interpretation)? Or is it wider, such as (for instance) having access to "in-law" Ancestors of your wife or other family members? Do you have access to "cultural" Ancestors, such as tribal Ancestors that you might in fact not be a direct descendant of, or Ancestors of a clan you were adopted by or married into? If you yourself were adopted as a child, do you have access to the Ancestors of your adopted family? Only of your adopted family? Essentially, can you "pick up" (or possibly even lose) new Ancestors through social and cultural means, or are they a fixed matter of descent?
Also, when do you not have access to someone who would otherwise count as an Ancestor? Heroes don't count for Ancestor spells, and presumably being devoured by the Bat would also make it... void. What about restrictive afterlives, like hells? In fact, what part(s) of the soul make up an Ancestor? If you summon an Ancestor who did well, do they come from the Underworld or from whatever nice afterlife they picked up? Does an Ancestor become unavailable if current reincarnated (presumably not?). If currently summoned by someone else (presumably yes?)? Can an Ancestor be summoned if it's also busy being a ghost (no, I think?)?