It's like some believe this hasn't been discussed and deliberated upon before and are surprised to hear such a strong scriptural based argument. They only have a vague understanding of the texts so when they hear something from someone that superficially confirms their bias they latch onto it without any investigation and trot out their beliefs as if they were self evident facts when in reality it's just them confirming their bias.Another explanation is that Cleophas was the brother of Joseph (Mary's husband) and Cleophas wife was also named Mary, meaning they were sisters-in-law, not biological sisters. Mary's biological sister was thought to be Salome, who was Zebedee's wife, the mother of James and John. This would make James and John the cousins of Jesus--and Peter, as a fisherman, knew and worked with James and John. Andrew, of course, was Peter's brother.
It appears that his mother, two aunts, and Mary Magdalene were the women at Jesus' crucifixion, and were also the ones preparing for his burial. (Mark mentions Salome by name at the crucifixion.)
When Jesus told John, "Behold your mother..." and Mary, "Behold your son..." the two had a blood relationship of aunt and nephew.