The Palestinians are descendants of the ancient canaanites. Most of the people in that region never left they just changed their religion at some point. This hasn't always been happening, in Ottoman times Christians Jews and Muslims peacefully coexisted in the region.
I mean, kinda? They're also heavily descended from 7th Century AD Arabic conquerors, but yes, many other natives may have adopted Arabic culture, language and religion at that time.
But Jewish culture is also derived from the Canaanite culture, with arguably more overlap. Jewish culture in the region can be traced back to at least the 9th Century BC, with the literal Kingdom of Israel. So the argument of "Well who was there first?" does not necessarily favor the Palestinians over the Israelis.
This has always been happening though. It's not like the Ottomans took over the region peacefully. It's been conquered and re-conquered by Babylonians, Egyptians, Greeks, Romans...
Palestinian culture is also derived from canaanite culture. Arabs are semitic people and follow abrahamic traditions. When places get conquered usually the ruling class changes but the lower class people stay in their homes and just change language/religion/identity. Usually the new rulers don't try to completely wipe out the inhabitants of their new land the way israel is doing with Palestinians
In what year are you talking about, because there is a lot of history in this part of the world. How far back should we go when we consider who is entitled to live where? 1000s of years? 100s of years? There were a lot less people living in that part of the world in 1945 if we just go back that far, there was room.for everyone. Overpopulation is also part of this.