a Catholic marrying a non-Catholic needs a dispensation for disparity of cult, and may also for pastoral reasons be granted a dispensation of form, if the marriage would be outside a Catholic Church, or even witnessed by a Protestant minister. This happened quite often in the 70s, in fact with my own sister, and sister-in-law, who both married sons of protestant ministers, one in a CAtholic Church and one in the protestant church, both witnessed by the minister fathers, and both with the proper dispensations so they are indeed validly married in the CAtholic Church. The both went on to follow their husband’s religions and raise their children in that faith. For that reason we have realized how mistaken that pastoral concern was, and it is not commonly done now. Speak to the pastor or deacon preparing you for marriage and ask these types of questions. I can’t think of a reason why two Catholics would want a non-Catholic minister to witness their marriage.