Expanding on Saint-Just's idea there and Segev's posts on the last page, I think what would realistically happen with inheritance (and therefore names) is absolute primogeniture. Your eldest child is your heir and gets a "strong" or "primary" name, while everyone else is expected to get married off in order to secure alliances and maintain social ties, regardless of gender. "One of you three needs to marry one of the four Dewmonts, so we're taking you all to a party so we can figure out which pair makes the best match." And if it turns out that two of the young men volunteer, the assumption is probably that they'll work out the question of child rearing between the two of them, possibly with a dowry from the wealthier family's parents to defray the costs. Possibly one of them transitions physically via alchemy, but doesn't switch their pronouns, since he's only going to be female-bodied 'for the sake of the children' and only as a temporary measure.