Can all the religions really coexist or will Christianity and Islam try to overtake them all?

No, they can not coexist unless they are in a secular community. If Christians truly followed there dogma, then Islam would overtake them. Jesus Christ taught this "Love your Enemies" and "Turn the Other Cheek" foolishness, while Islam has no problems killing the infidels. In a fight between one with a sword vs one with love, the swordsman wins.