It wasn't the Saudi family that got promises or fought against the Ottomans; they stayed neutral. It was the Hashemites who participated in the Arab Rebellion (Prince Faisal), and it was only after WWI that the Saudis then started to fight and defeated the Hashemites. The British then set up Hashemite princes on the thrones of Iraq and Jordan.
It wasn't the Saudi family that got promises or fought against the Ottomans; they stayed neutral. It was the Hashemites who participated in the Arab Rebellion (Prince Faisal), and it was only after WWI that the Saudis then started to fight and defeated the Hashemites. The British then set up Hashemite princes on the thrones of Iraq and Jordan.
Thanks for the correction!