Is it reasonable for Palestine to expect all descendants of refugees to be allowed to migrate to Israel?

There are 3 main demands that the Palestinians are making.
1. Return of previous borders.
2. Return of East Jerusalem
3. Migration of all descendants of refugees into Israel.

You may think of 2 as part of 1, but it is being treated by both sides as a separate issue. The first two items are reasonable and doable. The third would put a huge strain on Israel. The migration of a few hundred thousand Arabs would be highly disruptive, to put it mildly. We could go back and forth on the ethics and legality of such a move, but it is just not going to happen. By giving up on the third demand, the Palestinians have a chance of getting their country back. They would definitely gain support in the international community.