Yellow mobs outside Sardo Castle is a good place. If you have secondary/third classes that are lower than 63, then grinding the daily quest mobs in Pirhana Port in Tergothen Bay is also good cuz the items they drop are good for class-change dailies.
You do realize that leveling up those buffs past level 3 is going to take a HUGE amount of time/effort, even with consistent grinding, right? Just want to make sure you know what you're getting into if you plan on forcing the relationship buff(s) to level up.