Please post the Scripture(s) that identifies anyone (other than Jesus) as a biological son or daughter of Mary.
I'll save you some time. You can't. It doesn't exist.
If you're going to complain about other people's allegedly "unbiblical" beliefs, you lay yourself open to the charge of hypocrisy if you yourself seek to bind other people to beliefs that are not taught in Scripture.
Luke 24:10 It was Mary Magdalene and Joanna, and Mary the mother of James, and other women that were with them, which told these things unto the apostles.
Was He also denying He had a mother in the following verse?
Matthew 12:46 While he yet talked to the people, behold, his mother and his brethren stood without, desiring to speak with him. 47 Then one said unto him, Behold, thy mother and thy brethren stand without, desiring to speak with thee. 48 But he answered and said unto him that told him, Who is my mother? and who are my brethren? 49 And he stretched forth his hand toward his disciples, and said, Behold my mother and my brethren!
When the person said “thy mother and they brethren” he was obviously talking about His blood brothers or He wouldn’t have had occasion to point out that He also claims adopted “mother and brothers” as we are told we are adopted into the family of God. Jesus was clearly differentiating between blood relatives and adopted.
Galatians 1:19 But other of the apostles saw I none, save James the Lord's brother.
And please don’t come back to me with some “assumption” that Joseph had previously been married or that they were referring to relatives rather than blood brothers and sisters. It just doesn’t wash.