46While He was still speaking to the crowds, behold, His mother and brothers were standing outside, seeking to speak to Him. 47Someone said to Him, “Behold, Your mother and Your brothers are standing outside seeking to speak to You.”
48But Jesus answered the one who was telling Him and said, “Who is My mother and who are My brothers?” 49And stretching out His hand toward His disciples, He said, “Behold My mother and My brothers! 50“For whoever does the will of My Father who is in heaven, he is My brother and sister and mother.” Matt 12:46-50 NASB
In this passage it's one of two understandings.
In v46-47 the Jews have identified His mother and His brothers. They understand this is His family.
The context can only mean one understanding. The brothers mentioned here are Mary's other children.
Now, if you want to try and say that in vv48-50 that brothers means all the followers of Christ and that He had no biological brothers then you have to say that all the moms following Him means Jesus had no biological mother...and you know who that means.
The Catholic cannot have it both ways.
The people in vv46-47 are either Mary and His brothers or they are not and only mean those who follow Him as noted in vv48-50.
Are you prepared to say that?
Coming to His hometown, He taught the people in their synagogue, and they were astonished. “Where did this man get such wisdom and miraculous powers?” they asked. “Is this not the carpenter’s son? Isn’t His mother’s name Mary, and aren’t His brothers James, Joseph, Simon, and Judas? Aren’t all His sisters with us as well? Where then did this man get all these things?”. (Matthew 13:54-56)