Q: is it possible for an individual to be fully initiated to the faith during their Matrimony Liturgy? Could they receive baptism/confirmation and then first Eucharist at the same liturgy at which their marriage will be consecrated? I am referring here specifically to individuals who have completed the RCIA process and the annulment process and are ready to go “all in.”
A: I guess in theory it is possible, but sure not advisable. There’s no law against it, but there’s no liturgy to account for it, such as the one for the ordination of both a priest and a deacon in the same mass.
Correctly filling out the marriage paperwork depends on baptismal status. I don’t know how your bishop’s office would respond to this idea because the person, who is not Catholic right now, would be a Catholic at the time of the wedding.
I usually recommend take care of the convalidation as soon as possible. That will enable the Catholic spouse to return to the sacraments.
I surmise that this is done more commonly in mission areas where the priest is only visiting every so often, and he has to celebrate as many sacraments as he possibly can. But he has to cobble together how to do it because the liturgical books do not envision such a possibility.
I still think it’s best to convalidate first, and then handle initiation. But you’re closer to this situation than I am.