Theories

Balaam is the dark side of Kirell
When Argo kills Balaam Argo is resurrected. The only person which Argo mentioned training was Kirell. In addition, the achievement earned by gaining Balaam's trust is a broken mirror.

Quotes

 * "Me, I'm another version... of you. My resurrection... depended on you" - Balaam
 * "Anyways, seeing as how you're so calm at a murder site, I'd say back in real life we're the same, you and I." - Balaam
 * Balaam was just like the person in me that I did not want to acknowledge -Kirell
 * "You didn't betray me. You can't betray...yourself, right. It's just - you don't need me anymore. Congratulations, Kirell... You've carved out a...nasty part of your past." - Balaam

Philip is the dark side of Philio
Their names are very similar. Also, their abilities connect them both to the dead, Philip's mask blends him in with the undead and the undead avoids Philio.

The Philio in the real world isn't the Philio in the game
First, instead of Philio being a priest in the real world, he's a doctor. He also smokes in real life, which is something a priest shouldn't do. Philio in the game could be Charon disguising himself or Charon's follower, as mentioned by one of Kirell's answers.

Philio in the game also seems to know an awful lot about the main characters, especially Kirell. His abilities support this theory as well, being able to stay away from the dead if he pleases. He talks like he knows more than us, or like he knows something we don't.

In addition, this image shows him standing beside a picture of Charon, as well as some TVs which portray an eye (which can mean that he can see everything since he may be Charon or is a follower of his)

Quotes

 * "I'm just excited to see what sort of impact - those changes will have on you in real life." - Philio
 * "You're talking like you're gonna be watching over me." - Kirell


 * "Seeing you now, I think I'd want to keep my eye on you." - Philio

Charon is Philio
Charon have 2 masks and a backpack (and some paper from the backpack) on his profile. And we can understand he is a male from the sentences.

But the weird things is the philio have that backpack and papers on his profile. And that two masks is hanging from a cabinet.

That two maskes are weird too. The one of them have horns and smiling (seems like devil). And the other one just have a straight face.

That means Philio is Charon or Philio was sent to us from Charon (like a agent, like we saying on the day 4 with when we with Argo and Hilde:

"Maybe he's on the same side as Charon. Or he was sent by Charon ''to watch us." (Kirell)''

And another evidence is both of themtelling things about of Greek mythology. Charon telling us about of "River of Oblivion " and Philio says that on the last day:

"Heheh- this is what Orpheus must have felt-

travelling to Hades and back."

They are speaking about of same things, and don't forget: There is no any memory but Philio can remember a mythologhy (like Balaam remember some movies)

And another evidence is how Philio smoking. Philio smoking on the Randezvous # 2. The smoke hase a smiling face.

https://static.wikia.nocookie.net/7days-choose-your-story/images/c/ca/Photo5940734283939426532.jpg/revision/latest?cb=20190809152209

And Charon have a smoke-stick too (or something like that). And that smoke have a face too but it seems scared. But when Argo smoke, smoke has not any kind of face:

https://static.wikia.nocookie.net/7days-choose-your-story/images/d/d8/Photo5940734283939426540.jpg/revision/latest?cb=20190809152010

And last one, if you start with Balaam and then go to the Hilde and Argo, maybe you can see that:

When Argo killed Balaam and resurrect, Kirell talked with Philio and telled herself like that:

"So Philio already know that if Argo kill Balaam then he will be resurrected" (I can't remember exactly, sorry)

*** Probably that masks symbolizes the how Philio can be bad and good to us (evil or good) btw.

Philip is Kirell's dad
Philip may be Kirell's dad, because he didn't have a good relationship with Balaam, who is an alternative version of Kirell, plus he was violent but he didn't really know much about attacks, maybe because he only hit defenseless ones like young Kirell and her mother. His mask that gives in the ability to blend in with the undead, may represent him "hiding" among the good people in real life.