The two towns tell two halves of one story. Alençon is where the couple lived their whole married life, Louis as a watchmaker and Zélie running a lace workshop, and where Zélie died in 1877. Lisieux is where Louis moved with his daughters afterward, and where Thérèse entered the Carmel.
In Alençon the Sanctuary of Louis and Zélie receives pilgrims at the Martin family home and offers a walking route in the footsteps of the family: the Basilica of Notre-Dame, the church of Saint-Pierre de Montsort, which was their first parish, Louis's watchmaker's shop, the bridge where the couple first met, and the garden pavilion where Louis prayed. The sanctuary describes itself as a place for couples and families and runs retreats for married and engaged couples.
Good to know before you go: the Lisieux sanctuary puts Alençon 100 km (62 miles) from Lisieux, about an hour and a half by car, so the two fit in one Normandy journey. In Lisieux the crypt is open whenever the Basilica is, closing fifteen minutes before it. The family home in Alençon is shown to visitors on the Alençon sanctuary's own timetable, which changes with the season, so read its site the week you travel.