Holy fuck!!! You're pretty smartfrom what I can understand maxy and mary are completely different bodies, (after all velvet is pretty dead and you aren't that much) now I think that the whole plan does hinge on mary and maxy being pregnant at the same time in order to collapse both worlds into one (since velvet is dead he can't be the father of maxy's child and you also can't be the father of maxy's child since you're the father of mary's child) but I do think that the pregnancy has to happen seperatly, it's less change of personality and more exchanging with the twin from another dimension thing