We have been discerning with our Christian Candidates when they are ready and what their situation is, for instance, this year we have a baptized Christian preparing for Reception who is married to our catechumen. They will both be fully initiated at the Vigil. It is my understanding that by virtue of their initiation into the Church their civil marriage is “sacramentalized” with no need for further “convalidation”. Would that be correct?
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You are correct that the Catholic church recognizes the validity of the marriage of two non-Catholics – as long as one had not been previously married or some other impediment pertains. When one or both become Catholic, no convalidation should be done.
Incidentally, although many Catholics believe that the marriage of an unbaptized person to a baptized person is not a sacrament, the Church has never said that. It hasn’t said that it is a sacrament either. I’ve treated this in my book Inseparable Love.