Here's what I've got so far.
Now seems like a good time to learn the Additional Traits feat for Kori. He can get rid of Umbral Unmasking and learn Umbral Evolution. He's growing in power, taking control of his unruly shadow while also increasing the strength of his shadow magic.
Inspired Spell is a no brainer for him. It will let him use Mythic Power to cast any Oracle spells, whether he knows them or not, along with the spells he gains from the Dark Secrets Revelation.
Mythic Domain will increase his effective Oracle level by 4 when calculating the effectiveness of his Revelations. That's awesome; it will increase the AC and Stealth bonuses from his Cloak of Darkness, let him learn more spells from Dark Secrets, give him the Signature Skill (Stealth) feat early, etc.
[X] Kori Mythic Build
-[X] Mythic Feat: Spell Lore: Mythic (Invisibility)
-[X] Hierophant
--[X] Divine Surge: Inspired Spell
--[X] Path Ability: Mythic Domain (Shadow Mystery)
The Mythic version of Heroism is ridiculous. It gives most of the same bonuses as the Greater Heroism spell but also increase damage. It also feels very fitting for Mina.
Wild Arcana does for Arcane casters what Inspired Spell does for Divine ones. She'll be able to use Mythic Power to cast any spell from the Witch spell list.
The Mythic Hexes ability guarantees that anyone not outright immune to her Hexes will be affected for at least one round. Being able to put an enemy to sleep without them having a chance to save, even for just one round, is awesome.
[X] Mina Mythic Build
-[X] Mythic Feat: Spell Lore: Mythic (Heroism)
-[X] Archmage
--[X] Archmage Arcana: Wild Arcana
--[X] Path Ability: Mythic Hexes
The Mythic version of Haste is almost as ridiculous as Mythic Heroism. It makes recipients even faster AND gives them an extra Move Action. That's going to make the entire party so much more mobile during a fight.
Wild Arcana again. It's awesome.
The Flexible School path ability can open up some very neat options for Sirim. He's locked out of Conjuration, unfortunately, and the level of the effects being tied to Mythic tier is somewhat limiting, but the Divination school has some very nice abilities. I'm shamelessly ripping off Ellac's abilities from @Tomcost's great quest, Damned in Life (I recommend everyone should go read it!). The Inspiring Prediction buff alone is worth it.
[X] Sirim Mythic Build
-[X] Mythic Feat: Spell Focus: Mythic (Illusion)
-[X] Archmage
--[X] Archmage Arcana: Wild Arcana
--[X] Path Ability: Mythic Spellcasting (Haste)
Mythic Weapon Focus is a straight forward upgrade that makes Cob more likely to hit. Simple, but effective.
The Surprise Strike ability means he can Sneak Attack a target even when he wouldn't normally be able to, and that's in addition to his regular attacks.
Shadow Stealth not only makes Cob even better at stealth, it also gives him the ability to Teleport between shadows as a Move Action.
Imagine, he can Shadow Teleport behind someone as a Move Action, use Surprise Strike to Sneak Attack them as a Swift Action, then Sneak Attacks them a few more times because he's been Hasted by Sirim. It would be a devastating combo.
[X] Cob Mythic Build
-[X] Mythic Feat: Weapon Focus: Mythic (Light Blades)
-[X] Trickster
--[X] Trickster Attack: Surprise Strike
--[X] Path Ability: Shadow Stealth
Dual Path let's Gorok learn abilities from the Champion and Guardian paths. There are a couple path abilities that we might want him to learn later on that can enhance an Animal Companion, but I think he needs to focus on fundamentals for this first tier.
Fleet Charge is an additional attack that allows extra movement and it laughs at Damage Reduction, while Sudden Block is perfect for countering a hit that could otherwise injure Gorok or an nearby ally.
I'm not totally sold on Endless Hatred for Gorok's first path ability. It's somewhat niche, but where it applies, whenever we fight one of his Favored Enemies, it is very good. Considering how common Magical Beasts and Evil Outsiders are, it's not really too niche, though, and if there is ever an enemy you want extra bonuses against, it's Evil Outsiders.
[X] Gorok Mythic Build
-[X] Mythic Feat: Dual Path (Guardian)
-[X] Champion
--[X] Champion's Strike: Fleet Charge
--[X] Guardian's Call: Sudden Block
--[X] Path Ability: Endless Hatred