Nobody in Scripture is identified as a biological child of Mary except Jesus.
However Scripture does tell us Jesus had brothers and sisters.
Joseph kept Mary a virgin until He was born then they were free to consummate the marriage like any regular married couple....and that they did. Unless you're willing to again suspend the clear, normal meaning of the texts.
Scripture tells us that Jesus was her FIRSTBORN son, and since we know that those *ignorant sheepherders* can at least count, they would understand the difference between ONLY son and FIRSTBORN son.