Any vassal you marry into an NAP with can't faction,
Try marrying into, particularly in this case, all 26 vassals and their family. But yes, if one can actually manage to marry his offsprings into just half of these vassals things would get much better. Managing vassal revolts in a Pagan, or a Muslim realm is ridiculously easy nowadays thanks to this feature.
plus you get the 5 council positions+advisers who can't faction against you either. Between those, the majority of your realm's strength generally can't faction, and the remainder can be placated with spymaster/honorary titles/the essentially infinite gold any large realm has.
I believe this is true only for the realm with an 'Empowered Council' plus council voting for 'Declaration of War' is on 'Enabled'.