Love love love this game!
In future expansions, can widowed characters get remarried? And maybe as part of this - can siblings "inherit" their deceased elder sibling's spouses (levirate/sororate marriages)?
We are considering it. Not being able to remarry will force players to select the spouse carefully. However, remarrying might save a player from losing a game out of pure bad luck.
I don't think inheriting spouses will ever be a thing. Moving characters around the tree would cause quite some tricky issues. Also, I don't think it's something a lot of players would expect, and the features we add have to be chosen very wisely based on work vs impact.