Assuming it works the same way as real-life hybrids like ligers, only male half-elves would be guaranteed sterile (Haldane's Rule). Also Marcille can do body-shaping, soul-manipulating magic, I don't think they even need sex to make a baby.
Himitsu Airpri was something else. The Pretty Series from Pripara S2 onward has always been transparently lesbian to a hilarious degree, but Himitsu Airpri just went completely mask-off.