Why was Jesus's brothers and sisters considered half brothers and sisters?

Answer 1

Example: Let's say my mother gave birth to me and then something happened to my father and then later my mother married another man and had 3 more children. We would all have the same mother but different father's so we would be half brothers and sisters. Jesus' mother was Mary and Jesus' father was God (by the Holy Spirit). then Mary and Joseph were married and had children. Jesus and his brothers and sisters all had Mary as their mother, but Jesus' father was God and the other children's father was Joseph, making them Half brothers and sisters.