I hate to say this but Conrad is a better duelist than Cellia, Conrad has a real skill for bursting down enemys, Cellia has a dogshit skill for a bandit, Health is so much better than defense and is where bandits shine, boosting defense is not gonna help cellia. Cellia is good for getting more fairys though and I wish I had her.
Also Robert may be a decent healer right now for you, thanks to being male, but he's gonna drop off and become the worst healer in the game (alissa has 100 more attack at max, christopher about 50).
In general a archer and healer should be CC first, they get far more use and more out of CC than the others.
You have 4 Julians, so he will automatically be better than Katie when SU and CR which is very important for a great soldier. Most people do not get better soldiers than Katie and tend to be a bit biased.
Eventually you'll need to replace Calliope with Yuyu but that could probably wait a bit, also you'll want to replace Cecily but that can wait till you've got a better duelist.