Characters always tend to favor the familiar in the first position. The only way to have them change it up is to change their tactics. For example, If you set them to heal, they'll usually use the best healing familiar they have. On top of that, they don't seem to like using very weak familiars, which is understandable.
Also: A little bit later on, you get the ability to hit triangle to tell everyone to go "all out" for a few seconds or square for "all defend" for a few seconds. They will choose appropriate familiars for those two commands as well.
Ni No Kuni was originally a DS game so don't expect too much from the AI. The familiar in the first row tends to get picked first though I heard the "strongest" familiar or familiars matching the characters favorite genus are favored too.
Almost seems random to me which is a scary thought. The other night I had Oliver equiped with a level 91 Dynamite, a level 27 Catastroceros, and a level 4 Napdragon with no equipment that I was training up. Numorous times after switching to Swaine to steal I saw that wimpy Napdragon on the battlefield... Oliver, what are you thinking?!
Teenage angst has paid off well, now I'm bored and old.
They always seem to switch to the Dinoceros 3rd form for me. I thought giving them each 1 would be a good idea, but at one point it's all they would use unless I ordered some healing. Then I just realized I could use Sweat Pea to heal and let them bash face and I never looked back
I am the end and the beginning; I am the hand of madness. So says Mr. Stewart
I have Esther on keep us healthy and after she hit lv 35ish she stopped drilling all her mp in every fight. If you turn her to not use abilities and give her the danglerfish familiar in her first slot she gets by ok.
One more question, do I have to be controlling Esther to tame creatures? I'm using Ollie atm and not had a single tameable creature after about 7 battles.
the game gets very streaky like that. doesnt matter who youre controlling or who does the final blow to a creature though... if you get the lucky roll to make em tameable, then ya get the lucky roll. nothing more.
of course, you do have to switch to Esther to actually cast the serenade... but i dont think thats what your were asking.