There is an important doctorine that separates Christianity from Judaism and Islam. That is the Holy Trinity. It holds that God is three consubstantial persons or hypostases—the Father, the Son (Jesus Christ), and the Holy Spirit—as “one God in three Divine Persons”.  Without Jesus Christ being as one the person, the son of God, and the doctrine of Holy Trinity Christianity would not be possible.

Although, I am not sure about the teaching of Mormons and Jehovah’s witnesses. Many Christians don’t consider them Christians.