Asking Atheists: Where do you think the Jews and the Arabs came from?

I asked a question previously to Atheists which was if they believed Muhammad, Abraham, Jesus, Jacob, Moses, etc actually existed or were they just fictional characters, majority of which said that Muhammad and Jesus might’ve existed, but the rest they believed were fake, so according to Bible and Quran history, Abraham had two sons, Issac and Ishmael, so it’s believed that the Jews came from the bloodline of Issac while the Arabs came from the bloodline of Ishmael, so if Atheists believed that Abraham, Issac and Ishmael were fictional, then where did the Jews and Arabs come from?