The impression I got is that Ishmael would not partake in the priestly line and that a separate "world" was made for Ishmael. As for monotheism, I'm not so convinced except it depends on what is meant by monotheism. There is monotheism in the sense of pantheism or in the sense of panentheism or in the sense syncretism or.... Perhaps: "henotheism generally, monotheism internally (internal to the tribe)". The word "god" is said to be in part synonymous with "judge" or "ruler". The judges or rulers in China and the judges or rulers in the USA though they might have the same title, aren't 'gods' of the same people and are different gods. Of course, if A is bound to the laws of XYZ and B is bound to the laws of MNO, then they would each respectfully be judged by the respective rulers/judges of their countries. They could crusade each other's lands all they want about how there is only one 'god'--but they don't have the same 'god' in the sense of rulers/judges, just the same 'titles'.
How can there be strange or foreign gods and there be only one god? It is the potential for going off-road that is important to note. The neo-liberal twist on monotheism (i.e. which could be pantheism encrypted) might obscure this potential.
Did Abraham really go from polytheism to monotheism? Or did he simply eschew or reject worship of idols or external things, fully being aware that one could actually go after or worship strange, foreign or other gods or even worship one's own false or vain imaginations if one chose to?Panentheism is a form of monistic monotheism which holds that the being of God includes and penetrates all the Universe but unlike pantheism (see below) the universe is not identical with God
On the same note, if someone says "I love the prime minister". Who are they talking about? Justin Trudeau? John Key? Malcolm Turnbull? If the aliens say "Take me to your leader" to a crowd at an airport, they will likely be taken to ten or more different places. "Leader" doesn't specify whom. Thusly, a name is important.
On that note, royalty are typically addressed using plural. English speakers use you all the time (it is a plural word). Eloah is singular (more familiar rather than formal) word that can mean god, judge, ruler, angel, etc. It is said that "allah" and "eloah" might be synonymous. But is judge, ruler or angel a name? Is there anywhere in the Bible where the God of Israel says that is name is "God"?