So, if I have this right, Sanae-types can only give birth to Kanako-types and Suwako-types regardless with whom they mate.
Likewise, they can only be born through an uncommon pregnancy in another yukkuri from a Sanae-type, or straight-up from a Kanako-type or a Suwako-type pregnancy (from an egg).
Kanako-types and Suwako-types do not impregnate others or themselves get pregnant with babies of their own type.
Or: ZUN doesn't put even half a percentage of this much thought into doing anything Touhou. Likewise coming up with a hugely elaborate Old-World-of-Darkness-esque genealogy and crap is wasting entirely too much time that could be used for ease.