The two sperm in an empty ovum is the most likely thing to make sense... though there would still need to be mitochondria in the ovum because all mitochondrial DNA comes from mommy. That wouldn't be the same as having all 3 parents though, really - mitochondrial DNA doesn't matter that much (unless it's defective)

Anyway, I'm super excited for the kiddos!!! And your conversation with book_people was hilarious!