I'm having trouble with ELT too.
My team for doing Pro:
Krile is there for DC'ing Bar spells but she gets murdered in the first turn.
Should I focus all my energy to my team of Ludmilles to get a high enough TM to get Refia dualcast or focus my energy to leveling up my lvl 1 5 star Cerius until he gets dualcast, to replace Krile?
Well, with that HP is obvious that your poor krile will be slaughtered.
You need to give roles to your units and stick to a plan until end of battle.
First: All max 5 star units must have, MUST HAVE at least 3000 hp. Thats the base to think of survive the waves of attacks.
Your team is good. You can clear ELT with it but it need some build.
First Krile: Equip her survival edges (the dagger from FFZero event. If you dont have it, then equip her golden staff), 2 muscle belts, one HP+15% materia, and 2 HP+10% Materia (or any materia that gives you HP), and paralyna materia. Equip her carbuncle esper.
Krile's role in the battle: dualcast barfira and barthundara every 3 turns, and the other turns, dualcast cura or curaja (better cura for MP saving), and if Nian uses the attack that paralyzes, dualcast paralyna. Also the dualcast cura or paralyna you must combine it with dispel with Nian buffes himself.
Rain: Focus him in HP and DEF equip, only that. Equip him golem
His role in battle: Only undermine and throw healing items to other party members. Cast Provoke every time you want
Refia: HP and DEF equips. Equip Her a Jeweled ring for resistance to palsy
Her role: Embolden, Resurrection and healing.
Luneth and M.Fina: Heres the trick to end the battle fast because you wont win the HP race without a mana battery (like rosa and Noctis) and i WILL NOT RECOMEND to use a noctis friend. Because the damage will be disperse. The friend unit must be another Majin Fina.
Both Majin Finas only must cast Dystopia, for building her damage, and Luneth must cast Cut Through. And those 3 strikes must chain. Its only matter of practice but if you chain the dystopias (the easy part) with the cut through (the hard part), you can do good damage.
You have both units. You only must know how to use it and know the enemy patterns.