Your sons are men! Manly men!
They just want to love and be loved (in the butt).
Bad jokes aside, I fully support allowing the sov to marry anyone of any race or gender. As to how they make babies, magic. If sov's can make volcanos, they can probably manage a baby.
And if not, well, there's always surrogates. Or maybe they adopt?
Anyway, I see no reason why you couldn't have gay marriage amongst the children of the sovs, and still have those marriages produce kids. For one thing, it'd be deliciously progressive. For another, it'd be hilarious in screenshots, people would be so confused. For a third, I'd get a kick out of marrying a wizard sov to a fellow chick or dude.
A wizard's staff has a knob at the end indeed!