If a character were a multiclass Divine Hunter/Cleric (or inquisitor, or druid) with the Animal domain, I suppose that domain abilities would stack. Would the character receive the double ability score increase for her animal companion, or could she add her cleric level -3 to her hunter level for the purpose of determinating her animal companion's abilities? Would she add her domain spells to both her spell lists?
Would the character receive the double ability score increase for her animal companion, or could she add her cleric level -3 to her hunter level for the purpose of determinating her animal companion's abilities?
The latter - this has been pre-established in the FAQ. You can total your effective AC levels together, or you can have two separate animal companions for your divine hunter and cleric levels respectively. There is no reason why you would ever apply the stat bonuses for a single animal companion twice.
Would she add her domain spells to both her spell lists?
If you took the animal domain for both Divine Hunter as well as Cleric, then yes, but only insofar as it's detailed under the description of Divine Hunter.
In addition, the divine hunter adds the 1st-level domain spell from her domain to her list of spells known. She adds the 2nd-level domain spell at 6th level, the 3rd-level domain spell at 9th level, the 4th-level domain spell at 12th level, the 5th-level domain spell at 15th level, and the 6th-level domain spell at 18th level.
I don't think you can have two separate animal companions unless one class has a more restrictive list. That FAQ entry only says you can have separate ACs for Mounts and AC. Divine Hunter and Animal domain both have the full AC list, right?
You know, I was going to point out that the FAQ entry implies that it's possible to have multiple companion animals and it doesn't stipulate that one must be a mount (or otherwise restricted). However, I then took a look at the description of animal companion for both druid and hunter:
If a character receives an animal companion from more than one source, her effective druid levels stack for the purposes of determining the statistics and abilities of the companion.
This would imply stacking your animal companion levels is indeed mandatory whenever possible (at least when using an animal companion ability that somehow references the druid class ability, which I believe every single instance of the animal companion ability does). Good catch!