Grand Alliances are coalitions of factions who share a overall philosophy and goal. They don't even have to like each other.
Such as Order wants to be free from the evils of the dark gods and build their civilizations , they don't want to be Undead under the control of nagash and they are not rampaging Destroyers who want to fight or eat everything
These factions can come into conflict with one another, either due to their moral views, how they go about spreading and growing their civilization. Or do to their individual faction or sub-facion's goals.
Conflict can even occur within the same faction. such as between the knights Excelsior and the hallowed Knights.
Read the fyreslayers lore, They are without a doubt order, they are a complex civilization. The only reason they are mercenary at all is to resurrect Grimnir. You can read there lore on the Lexi
sylvaneth are also order, believe it or not they are a civilization. composed of various Glades, Kingdoms and Clans. they also represent natural order.