A prophecy from Psalm 69:8-9, [I am a stranger to my brothers, an alien to my own mother's sons; for zeal for your house consumes me, and the insults of those who insult you fall on me.] In John 2:17, [His disciples remembered that it is written: "Zeal for your house will consume me."]
The Greek for brother is Adephos and that is the word in the Greek translated "brother" in Matthew 12:46,47,48,49, and 50. Also Matthew 13:55 where his brothers, alluded to in Psalm 69, are mentioned by name: James, Joseph, Simon, and Judas. Also in Mark 3:31, 3:34, 6:3; Luke 8:19,20,21; John 2:12, 7:5, 7:10; Acts 1:14, 12:17, Galatians 1:19.....all of these translate adephos as "brother".
The Greek word for cousin is "Anepsios" and you will find it in Colossians 4:10 describing the cousin of Barnabas, Mark.
If Matthew, Mark, Luke and John....and Paul wanted you to believe that James, Joseph, Simon, and Judas were cousins... they would have said so.
What is lost in the translation is the incorrect teaching of your church with regard to Mary's perpetual virginity that forces you to ignore scriptural truth.
Of course Jesus never said "adephos" since he did not speak in Greek , but rather in Hebrew and Aramaic.
Perhaps someday archeologists will uncover "Hebrew mathew" or the other original Gospels that the original Jewish Christians had.