This is idiotic on multiple levels.

First of all, it's NOT up to Palestine. This is not some ideological statement, this is just reality. The geopolitics works by de facto control, not by some idealized notion of righteous ownership. If that was the case the native Americans would be decided US foreign policy, but that's not how it works now is it? The cold hard reality is that Israel is the true sovereign of the land, and neither Palestine nor any country can do anything substantial without Israeli approval. Therefore, they're the ones who actually have the deciding power. Whether you agree with it or not doesn't mean anything, that's just the way it currently is.

Second of all, Palestine did NOT exist before the 1930s. There has never been sovereign Palestinian state in history. The modern Palestinian national identity was formed in the 1920s as a reaction to Jews getting serious about establishing Israel. Before that point, there was no such thing as a Palestinian identity. The Arabs in the region were indistinguishable from the other Levantese Arabs. The Arabs in what is now Lebanon, Jordan, Syria, and Palestine have the same exact history, dialect, culture, food, religion, and so on. They're called both today and historically as Bilad Al Sham which means the Levant nation in Arabic.

What we think of modern Israel and Palestine are both inventions of the British. The borders, for example, like with the other countries in the region are nonsensical and drawn randomly. The Arabs there did not see themselves as Palestinians back then, but as Arabs that were a part of the Arab nation (ummah al arribiyah). If it were up to the Palestinian Arabs back then, there wouldn't be any borders because these borders were dividing a bigger nation. The British promised both the Jews and the Arabs a state, and this annoyed both which caused them to start segregating and fighting each other trying to make sure that the other one doesn't get a state. This eventually led to the 1948 war when Israel did end up declaring independence.

Finally, Christians, Jews, and muslims most certainly did NOT live in peace. This delusional idea is only held by ignorant Westerns who have no understanding of the region's history. No matter how far back in history you go, there's always a strong presence of revolts, wars, and ethnic cleansing in the region because whichever religious group ruled the region oppressed the others. For example, when the Turks ruled. They applied islamic law which treats non muslim monotheistic believers (polytheism is punishable by death) as second class citizens. Non muslims are forced to pay a tax that muslims don't have to pay, they're forced to observe islamic holidays, and they're saddled with a lot of restrictions that muslims don't have.

This already makes everyday life very hard, but the exclusively muslim ruling class would made sure to keep minorities down at every turn. For example, whenever the Ottomans had war, they would force entire towns near the frontlines to evacuate, but they only allow muslims to return afterwards. The property and wealth that was left behind would be possessed and distributed among muslim soldiers and officials as spoils of war. The same goes for the places that got conquered, except the non muslim women and children there would also get ensalved. This type of treatment is the reason why the Greeks, Serbs, Armenians, Assyrians, and so many other minorities revolted against the Ottomans and ended up getting genocided as a result. But it's not just the Ottomans, the Malmuks before them as well as the Umayyads, the Abbasids, the Crusaders, and so on all engaged in similar behavior. You would be hard pressed to find any sustained period of time in this region's history that didn't have oppression, war, or violence.

Palestinians have no power so they can't decide.