Has anyone got any tips on how you can level up the Eidolons? I am at Chapter 5, I just returned to Rubrum and my entire class are a mixture of level 26 and 27.

Can't say I have used the Eidolons much to be honest (I have only summoned Ifirit) as I find the Triad attack is a lot more useful in most combat situations then risking sacrificing a party member.