The spelling difference doesn’st mean squat- you realize there’s not even a single “correct” spelling using English letters for “Osama bin Laden aka Oussama bin Laden, Usama Binladen,” or for “al Qaeda aka al Qaida aka al Qehdah, aka al Queada aka Alqaeda,” the prophet “Mohamed aka Mahammad aka Mohammed aka Muhummad aka Mohamad aka Mahammed aka Mohammad aka Muhamed,” or even for the “Koran aka Quran aka Q’uran,” don’t you? If they can’t agree on what English spelling of the Holy Q’uran to use or what version of Muhammed to use what makes you think they have settled on one spelling for Ismail? One spelling for a given person’s name? That’d be a first! They may be consistent spellers when using arabic script but when sounds are translated phonetically Arabic words no standardized English spellings.
It’s Ishmael in the King James version of the Bible.