Moslems have disputes whether its Isaac or Ishmael, as the Quran only states that it is a son of Abraham.
Islam does not reject Jesus. In fact, Moslems accept all of the Prophets descended from Adam, Noah, Abraham, Isaac and Ishmael- and that’d include Mohamed, the last one. Its Judaism which rejects Jesus, at least in the past.
Agreed though, it’d be really nice if they could live harmoniously together, since none of the Abarahamic religion can be proven correct/wrong till God decides. They should unite on their basis of connection to Abraham and monotheism, and to Adam and the existence of God, Judgement, Paradise, Hell and Satan.