Mary in the bible is called the mother of Jesus. Although Jesus is fully divine, Mary is never called "Mother of God" in the bible. Joseph was the legal father of Jesus but not His biological Father:
“Now Jesus Himself began His ministry at about thirty years of age, being (as was supposed) the son of Joseph, the son of Heli,” (Lu 3:23 NKJV)
Yes, He was popularly supposed to be the son of Joseph, but remember what Gabriel said to Mary:
“And the angel answered and said to her, "The Holy Spirit will come upon you, and the power of the Highest will overshadow you; therefore, also, that Holy One who is to be born will be called the Son of God.” (Lu 1:35 NKJV)