“Where do the Shias fit in?”
Muslim Brotherhood (Sunni) is Egyptian in origin but financed and exported with Saudi money. Most of Saudi Arabia is Sunni with some Shia areas near Iran.
Hamas is also Sunni while Hezbollah is Shia. Iran is Shia which is why they fight against the Sunni ISIS, which descended from the Muslim Brotherhood.
And none of that matters when it comes to fighting the infidel