I have mentioned already that the deities in Angadurgh will be fickle, egotistical and not particularly reliable (although still very powerful).
I see this playing out in a way that divine characters will have to make “concordance” checks, much like those for artefacts. Being “in concordance” makes it very likely that ones divine powers will work as usual. Being out of concordance will make it unlikely. I would actually recommend that players build hybrid characters, so that they can at least draw from their non-divine class when the gods fail them.
The mechanic would be based on a modified d20 roll at the beginning of each encounter (or before using any divine powers such as rituals outside of encounters). If the roll succeeds, all is well, divine powers will work as expected. If the roll fails, then divine powers will be “variable” in result. A roll on a table will determine what happens when a power is used. Results will range from “works as usual, but with a minor non-mechanical side-effect, through simply not working at all, to wreaking significant damage and/or conditions to the caster and those around her.
As for following the wishes of the deities, the DM will have to follow/create plotlines for them. Using their personalities, and some pattern of events taking place in the heavens, one can create a dynamic that would have the Gods demanding certain actions of their mortal followers as they (the deities) jockey for position, carry out vendettas, or vie for prestige in their heavenly realms.