This is a really neat concept. Five children born of sperm donation connect with each other and try to meet their bio dad. The two narrators, 15-year-old Milo and 14-year-old Hollis are the children of lesbian partners. One of Hollis's moms has died, and Hollis has been in denial about her grief. The quest helps her connect to her surving mother, and also to her newfound half-sibs. The relationships felt believable to me, and I like that the ending was ambiguous. It wasn't a cliffhanger, but I'd like to see a follow up.
They'd had the Sex Talk, as in, "Most babies are not conceived in a petri dish."
Though the protagonists are middle grades age, the story reads like YA.