This suggestion is related to the coop player marriage and the second heir thread, but can also be a stand alone feature.
It would be great to incorporate adoption from kids inside or outside your own village to your own family. This could be done through pop ups on season start, like we already have in the valley prompting you to make a decision of taking in a foster child (in case you have space in villager housing you could also get prompted to assign the foster child to an existing household from your village other than your own household).
This could solve the question on how to continue the dynasty in case player marriage gets incorporated or if you rather want to not bother with NPC marriage.