My family is Catholic. My sister has been dating our cousin (my mom’s older brother’s son). Can they get married?
Blood relationship (consanguinity) in the direct line (such as father & daughter, mother & grandson, etc.) or in the indirect line for those related as closely as first cousins is an impediment to marriage (cf. Canon Law, 1091.2). However, such an impediment may be dispensed by the bishop of your diocese. Your sister may wish to contact her priest for more information.