I don't think you even need to prioritize factions, necessarily. Let's consider that adult red dragon - Vorthinax, She Who Rages Against Death.
Vorthinax is both adept with curse-magic, and suffering a terminal mental illness. The further along that disease progresses (use a catastrophe die, rolled once per in-game month), the more erratic and more powerful she becomes. So as the catastrophe die drops to a d6, she gains resistance to all weapon damage (as barbarian's Rage), and the Unstoppable Rage feature. And then she shows up and wipes out a village, bellowing in Draconic.
As it drops to a d4, she gets an extra attack, and immunity to the charmed and frightened effects, as well as to any effect that would put her to sleep. Additionally, she gains resistance to psychic damage.
Finally, if the catastrophe die hits 0, she gains the traits of an ancient red dragon, along with all the effects she's previously gained, and will attempt to wipe out all life within a 50 mile radius of her lair...starting with any opposing power centers.
The key is that you have to let the PCs know the clock is ticking on all of these - that some of these threats are immediate and deadly and will get much worse if ignored. Light a fire under them that they need to get ahead of things. You can do that with proper rumors and proactivity, but if you don't telegraph any of this information (not the mechanics, but the "This is going to get bad" part), then don't be surprised when your PCs get salty about it when