Does any of them have to be predominant? Co-existing would work just fine. The thing is, Muslims, Jews and Christians used to live in peace in the Palestine
All of the three faiths demand predominant obedience from their followers, and inculcate the mindset that any other faith is false, defective and a sham. Kinda difficult and strained at best to co-exist when each faith preaches strongly against all others. I hate to burst your bubble, but the Jews and the Muslims have been at each others throats for several thousands of years. Whatever peace shakily existed was between wars when either side was regrouping or working secretly against the other. with either Britain, France or the USA. Christians stood back and watched the ongoing fracas while waiting for a winner to emerge. It hasn't happened yet.
I've met people who do believe that it is the same God in all three, from all three religions, and from historic point of view it definitely is.
Again I am sorry to disappoint your beliefs, but there is no written history - as opposed to opinion - that I am aware of (and believe me I have studied it) that proves each of those three faiths to believe in the same God. Their own holy writings vehemently deny that any other faith practice can worship a true (in their eyes) deity unless that faith is forsaken for the self-proclaimed "true" one. By their own holy writ, each excludes the other. I cannot imagine what history you have read that contradicts this fact. I sincerely would like to know how you come by this info, as I maintain a lifelong interest in human faith towards deity. THere are many offshoot belief systems which foster the ideal of syncretism - the melding of various faiths into one supposedly harmonious belief. Bah'ai is one of those, with it's basis in Islam. Sadly, the other Islamic sects murdered the founder of the Bah'ai faith........and his (Baha'ullah) writings took root in Islam, with vestiges of Judaism, Christianity and a few other bits and pieces. The problem with any syncretistic religious structure is that there is no definitive standard. Things might be right or might be wrong, depending on which melded-in faith one wishes to cling to.
Those believers of whom you speak are denying their own faith's commandments. I would earnestly love to see peace and common acceptance among all Jews, Muslims and Christians.............but it just ain't so! Your version of the origin of these faiths is interesting and has some fact to it, but many specific and critical events are overlooked that have created completely separate faith structures.