Assess everyone's power.

Not everybody at Castle Phoenix serves to fight, and it becomes even more complicated when one compares a class granted by the God of Adventuring to a monster. See, when a person takes upon a class, they receive what is effectively a divine boon that grows in strength as they practice their craft. That doesn't mean somebody requires one to get stronger. You can still light weights and gain muscle without levelling up a class. Monsters, however, have a natural boon built into their genetics. They tend to be inherently stronger than an ordinary person regardless, as well as having innate special abilities. For example, a succubus may not have a class, but they're resilient, strong, and have all sorts of different unique powers, such as Linzeri being able to make a man instantaneously hard by a simple touch of her finger.

Some say that in the long run, at the highest level of things, level should not even be considered as part of the equation. There are far too many variables. An ancient dragon has no class, yet one can completely wipe a party of high level adventurers with ease. Some grant these monsters what's called an Estimated Level, which is an incredibly broad estimation on how the monster may compare to somebody with an actual GOA class level. As one might expect, the scale is very loose.

This Estimate Level doesn't necessarily only apply to monsters. Some people with very unique abilities may equal the a high level adventurer with a class despite not having a class themselves.

That being said, you take note of what you do know, whether it matters or not.

Niki
10th Level Warrior (Stormwall) - Possible +2 from Rite of the Sun [12]
Amara
10th Level Cleric (Archpriest) - Possible +1 from Mana Mutation [11]
Eva
10th Level Mage (Universalist) - Possible +1 from Magic Eater [11]
Snow
10th Level Rogue (Kunoichi)
Vivilia
13th Level Mage (Transmuter) - Possible +2 from Unique Bloodline [15]
Thomas
8th Level Rogue
Bekram
9th Level Warrior
Summer
7th Level Warrior
Taiga
8th Level Warrior
Lynx
9th Level Rogue - Possible +2 from Rite of the Sun [11]
Fang
9th Level Rogue
Lalarin
9th Level Monk
Malakae
9th Level Mage - Possible +3 from Gold Dragon [12]
Delphi
10th Level Dark Fairy (???)

Alice
9 EL
Peony
6 EL
Jelly
5 EL
Dajy
13 EL
Klava
6 EL
Raleza
6 EL
Brizi
6 EL
Vodrani
8 EL
Stax
8 EL
Koblix
6 EL
Mipa
8 EL
Chula
6 EL
Chini
5 EL
Chila
5 EL
Patricia
4 EL
Sen-nu
8 EL
Meladarai
EL 9
Fava
EL 5
Linzeri
EL 8
Cat
13 EL
Shivra
9 EL

You
10th Level Demon King - Possible +5 from Bunny Hop, Kitty Sense, Invisible Ties, etc [15]
(This one is by far the most subjective. It may be even higher given the potential of your abilities and your unique physiology.)

You hesitate to attribute an Estimated Level to Luna, Laira, and Dixby, as they aren't combatants but craftspeople. Queen Catherine is in a similar boat. She can fight with a sword, though she isn't a warrior.

By your estimation, Bek, Lynx, Fang, Lala, and Malakae are rather close to reaching 10th level. They must be deeply considering what they'll take as their elite classes.

Nyllia and her party (Bill & Phil and Zazra) haven't returned yet, so you're not certain what level they are now.

Speak of the devil, however...

That night, after dinner but before anybody has gone to bed, the party in question arrives at the front gates. You head there yourself, as does Eva, Amara, and Niki, to greet the famous adventurer Lady Nyllia Tesgella as she arrives home at last. However, the her face is not one of stoic nobility. She looks concerned, and understandable so. Just as you did earlier, you explain to the woman all that happened, and that she doesn't need to worry.

Immediately after, Nyllia drops to a knee and slams her two-handed sword deep into the ground. "My King. I apologize that haste did not return me home swiftly enough to defend these walls."

Bill speaks up with a hand on his plated chest. "We were off in the hills, slaying a manticore."

"Stand," you command. After Nyllia slowly rises, you place a gentle hand on her cheek. It's strange to see someone you know to always be so confident and strong look to you with such defeated eyes, and you don't like it. "We were victorious. When people are sent away from these walls, they aren't expected to magically teleport back in a moment's notice. You did what you should have done. Because of you, a beast was slain, and while you were gone, we slew many more. Now stop looking at me like you did something wrong."

Finally, she smiles. "Oh Kyle. Of course. I should not have spoken so foolishly."

Zazra the oni swings her mighty club back over her shoulder. "I tried to tell her! If we weren't there to slay the manticore, people would have died."

Nyllia
13th Level Paladin (Templar)
Bill
8th Level Warrior
Phil
8th Level Warrior
Zazra
8 EL

"Well, I was just about to head to bed, so get some rest, guys." You gesture to the area around you. "Then we continue cleaning and fixing everything up. All things considered, we ended up pretty good. Not much was destroyed, and our people were hardly injured by the end. We got word the invasion was coming, and then in the middle of it, two members from the Circle showed up and helped. It looks like the tables are turning. Soon, we'll be the invaders, and it won't matter whether or not Elok Daven knows we're coming."

On your way back to the castle, however, you run into Delphi. She seems to be acting strangely.

These levels were mostly for fun. Remember that power levels are bullshit, and fights are a lot more complicated than just comparing numbers. Still, this gives a general idea of everyone's strength, whether or not they have a class. And in time, there may even be ways to empower monsters beyond their ordinary limits.