Its not wise to give parlament the power to make a king--for then, they will have the power to unmake a king..

is allegedly the advise that was given to Vicky when she wanted Prince albert to be make king (so they could be co-rulers.)

William and Mary each had claims to the throne, they were a rare case of being co rulers.

it also depends on rules/laws for kingship.

some 'crowns's don't recognize a daughters right to rule on her own, she must marry a royal prince to become queen --
but some traditions (UK) allow a woman be a prime ruler, (and cast her husband into a secondary role)

my other obsession