that word brothers is sort of problematic in the light this is this question of dogma driving driving interpretation again. so, what we have is the greek word adelphos, which the primary meaning is brothers. anybody looking at that text and seeing, are these not the adelphoi of jesus? would say, are these not the brothers of jesus? the apocryphal gospels tried to clear up the mystery by presenting the brothers and sisters of jesus as simply the children of joseph from a first marriage, but the apocrypha and the catholic church don t always agree. it is the belief of the church that mary remained a virgin after the birth of jesus the doctrine of mary s perpetual virginity. the brothers and sisters of jesus referred to in the gospel were his cousins. but that s piety driving the interpretation of the thing so that adelphoi is translated, for example, in traditional catholic circles, it s understood as cousins rather than brothers.