Note that French succession had a longstanding ban on female descent; Napoleon continued that OTL, and likely would ITTL as well (since changing it would be difficult, and he's likely to continue to hope for a son for some time after his daughters are born). So they aren't heirs to the throne, but could be wives for ambitious generals and/or client kings (in the same way that Murat married one of Napoleon's sisters OTL).
I'm sure that Napoléon would've found a way around that. I know he planned, that if the king of Rome was born female, to marry her to Louis-Hortense's son.