To clarify, in my hypothetical scenario your opponent cites the following verses:
"53 And when Jesus had finished these parables, he went away from there, 54 and coming to his hometown he taught them in their synagogue, so that they were astonished, and said, “Where did this man get this wisdom and these mighty works? 55 Is not this the carpenter’s son? Is not his mother called Mary? And are not his brothers James and Joseph and Simon and Judas? 56 And are not all his sisters with us? Where then did this man get all these things?” 57 And they took offense at him. But Jesus said to them, “A prophet is not without honor except in his hometown and in his own household.” 58 And he did not do many mighty works there, because of their unbelief."
and then says, "See! Scripture plainly states Jesus did not have biological siblings, and there is no reason at all to think otherwise outside of certain biases that have been forced onto the text," merely because they read the words "brothers" and "sisters," and assume a meaning other than "born of the same father and/or mother" applies to them. Would you say there is nothing further required from your opponent to prove they are right?