They're torturers, so I get more of an Intimidate vibe from them as well. I don't think we should invest two feats into social skills, though. Multiattack I would favor.
Perhaps light spells and searing light should deal lethal damage and deal damage as if it were undead?
I'm going to say Diplomacy 3, Intimidate 3, Listen 2, Sense Motive 2, Spot 2. Then give them Negotiator and Skill Focus (Intimidate).
Hmm, I thought of the harassment they do as more like Intimidation, but I can see Bluff. Or we could add Bluff, go with 2 ranks for everything, and take Persuasive insteand of SF (Intimidate).
Perhaps light spells and searing light should deal lethal damage and deal damage as if it were undead?
Updated.
Organization: Solitary?
Alignment: Always neutral evil?
Advancement: 4–6 HD (Medium); 7–9 HD (Large)?
Celestial stags are x feet long and weigh x pounds.
Neutral evil seems the right alignment to me.