What level of proof would be needed for a person whose ancestors lived in Mexico and who claims to be a descendant of the Marranos to be considered Jewish for the sake of marriage? Or are all such people required to do tevila for the sake of conversion prior to marriage in an orthodox setting?
I think this question may not be fully answered by the MY answer to the more general question “Am I Jewish?” because there is historical support for the existence of Jews in (and then from) Spain who lived outwardly as Christians.