@CarlMuckenhoupt
I don't know. I feel like a good lawyer could make a marriage which was undertaken after death stick, possibly forever because you can't die twice. It's not, "until death do you part and ever after." It's pretty clear that death is an event which severs the bonds of matrimony, not a state which prevents it from being undertaken. So while I would agree that a vampire couldn't expect to remain married to their mortal spouse after becoming a vampire, there's no reason to suppose that a vampire couldn't enter into a contract.

It does raise the legal question of whether or not someone who is dead can give consent. I am no lawyer, so I can't cite relevant case law, but anecdotal evidence suggests to me that the dead can't give consent under many legal systems. I wonder, however whether that would change if vampires were presented to the court. Is consent premised on being alive or on intelligence, as seems to be suggested by the fact that children can't give legal consent to many things. Maybe a zombie couldn't give consent but a vampire could?

However, you're on much firmer logical ground for the idea that a vampire would just never turn into a werewolf because they're already dead. I like it. Werewolf transformation is clearly something which relies on the life of the subject, as you say. It's not like werewolf corpses transform into dead wolves every full moon.

All that said, it's not airtight. Maybe the reason werewolves return to human form upon death is that death removes the curse, but thereafter they would be susceptible to it again. Maybe undeath isn't death. Maybe magical creatures aren't subject to the same rules as mere mortals. Maybe vampires aren't really dead. There's wiggle room for other interpretations, is all I'm saying 😉