If the couple are baptised Catholics but not regularly practicing the faith, can they celebrate their marriage in the church?
This is a delicate question, that may well be raised by the priest at the pre-nuptial enquiry (interviewing the couple about their wedding plans). Clearly, for a church wedding to be authentic, some measure of "belonging" within the Catholic community is required.
But who "belongs in the Church"? Who are to be regarded as practicing Catholics today? The phrases seem to cover a wide spectrum of levels of "belonging", from regular attendance at Mass each Sunday, to a looser or occasional participation at Church functions - say at weddings, funerals, anniversaries and major feasts, and a general acceptance of Catholic faith and morals. It would always include a personal trust in Jesus Christ as Saviour, allied with some sense of God's presence in our life, and some linke with the Catholic community of faith.
If this description of Church membership applies to even member one of the couple, then a Catholic sacramental wedding is possible. The priest interviewing the couple will probably urge them to share in the life of their local parish as a married couple. This is part of his pastoral duty, helping them prepare for sacramental marriage.
Some declared intention of future taking part in the life of the church is normally a requirement during the couple's "Prenuptial Enquiry" interview with their priest.