Most patronage of this kind grows from devotion, not from a decree. St. Joseph's title as Patron of the Catholic Church was formally declared by Bl. Pius IX in 1870; describing the Martins as patrons of marriage is a widespread and fitting custom, not an official title.
Each of these saints has a place a couple can go. The Martins are honored at Alençon in Normandy, where the church of their wedding is now a basilica and has kept a reliquary of the couple since their feast on July 12, 2025, and at Lisieux, where their original reliquary rests near their daughter St. Thérèse. The Beltrame Quattrocchis were married at the Basilica of St. Mary Major in Rome, and St. John Paul II is buried in St. Peter's Basilica. St. Joseph's Oratory in Montreal is the great North American shrine of St. Joseph, and Sainte-Anne-de-Beaupré in Quebec has honored St. Anne since 1658. In 2023 the Church also beatified an entire family, Józef and Wiktoria Ulma and their seven children, of Markowa in Poland.
Good to know before you go: none of these places requires anything of a couple except time. Many bring a written intention or renew their vows quietly at the altar, and an anniversary is as good a reason as a difficulty. Asking a saint's intercession is asking for prayer; the saints lead to Christ.