Hm.. where would this be set in? A specific area, I should hope, so as to limit communication barriers such as language, time and space?
Would the Gods take any direct actions within the realm, or only through their angels or demons?
Would demons be only masses of "evil or angry emotions", or also :
-lustful feelings, such as greed, carnal lust, etc,
-lack of feelings, such as laziness, emptiness, futility, etc,
-feelings derived from loss, like sadness, grief, abandon, vengeance, etc,
-feelings derived from physical manifestations like physical pain, sadism, death, etc,
Would demons also have a chance to be composed of mental states like madness, confusion, obsession, etc?
Would the demons favor any side, or be chaotic neutral in alignment?
Would the demons exert direct control over creatures, or only influence by presence?
Would demons be capable of independent thought?
Would demons be able to possess a creature?
If the 2 questions above are answered positively, would demons be able to communicate with humans apart from possession, would humans be able to communicate with demons?
Are demons controlled by the gods who made them, or are they given free reign?
If they are controlled, can they break the chain of binding?
More questions may be in order, but for now this is all I have.
I only ask them because I'm interested, and because you didn't specify quite a lot of things in your post.