What negative modifiers do they have? What factions?
I am still tweaking it for Crusades. Ideology, Conquest Victory Goal and Ripe for Conquest can all be pretty hefty negatives atm (depending on personality choices for the AI). I also forgot to tweak the min relations to declare war value to account for the bigger relations (should be -12 think it is -4 in vanilla), I have fixed this my end as well as tweaked some modifiers too balance it out a bit.
Are you Opening Boarders, Declaring Friendships, Refusing Demands, Giving Gifts? All helps alot tbh.
I am still learning Diplomacy in Crusades tbh, I am finding you have to be alot more active and "free giving" if you are opposite Ideologies or considered Ripe for Conquest, both of these on one AI can be pretty brutal to your diplomacy. Which it should be really, might be a tad over done, will have to play tes tmore to really get a feel.