Youcat commented through CCC - Question n. 81.

YOUCAT Question n. 81 - Did Mary have other children besides Jesus?

(Youcat answer) No. Jesus is the only son of Mary in the physical sense.     

A deepening through CCC

(CCC 500) Against this doctrine the objection is sometimes raised that the Bible mentions brothers and sisters of Jesus (Cf. Mk 3:31-35; 6:3; 1 Cor 9:5; Gal 1:19). The Church has always understood these passages as not referring to other children of the Virgin Mary. In fact James and Joseph, "brothers of Jesus", are the sons of another Mary, a disciple of Christ, whom St. Matthew significantly calls "the other Mary" (Mt 13:55; 28:1; cf. Mt 27:56). They are close relations of Jesus, according to an Old Testament expression (Cf. Gen 13:8; 14:16; 29:15; etc.).    

Reflecting and meditating 

(Youcat comment) Even in the early Church, Mary’s perpetual virginity was assumed, which rules out the possibility of Jesus having brothers and sisters from the same mother. In Aramaic, Jesus’ mother tongue, there is only one word for sibling and cousins. When the Gospels speak about the “brothers and sisters” of Jesus (for instance, in Mk 3:31-35), they are referring to Jesus’ close relatives.

(CCC Comment)

(CCC 510) Mary "remained a virgin in conceiving her Son, a virgin in giving birth to him, a virgin in carrying him, a virgin in nursing him at her breast, always a virgin" (St. Augustine, Serm. 186, 1: PL 38, 999): with her whole being she is "the handmaid of the Lord" (Lk 1:38).      

(The next question is: Isn’t it improper to call Mary the “Mother” of God?)