Just my opinion here, and it's your novel, and you know a lot more about it than I do, so take my suggestion with that in mind.

I think you should make Protagonist 3 your main character and make P1 and P2 side plots. She has the clearest goal and the best opportunities for ongoing obstacles.

With that in mind, I'd write the hook from her perspective: Fresh from civil war, the weakened land of Wellestria is threatened by a neighboring empire. A federation made up of noble families has replaced the former Wellestrian monarchy. Protagonist 3 must unite Wellestria and face this new enemy, but she is thwarted by two feuding noble families who refuse to set aside their hostilities.

Something like that?

Cheers,
Michelle