| I generally leave it up to the player to come up with why a given skill should count towards a success.
In the case of Religion, it makes sense if done prior to the Intimidate as the knowledge learned can shape what tactic is used to scare the NPC into talking.
In the case of Heal determining if the wound was lethal, I don't see how that could tie in as part of persuading the NPC to talk. I would not have counted that skill use as a success unless the player came up with an entertaining reason why making sure the guy wasn't going to die soon would be a convincing reason to talk...
As to having PC's stay out of the challenge. One premise of the system is to let everyone play without penalty. But if they don't want to join, don't force it.
I run single PC skill challenges as a 'compex skill check' instead of using obsidion. But techincally you could just go with 2 successes in 3 checks as a single PC challenge.
__________________ "Words take on strange and wonderful powers when they are written down.
Context and intonation disappear, and the words sit in a void to be construed according to the mood, intelligence and socio-political leanings of the reader."
--- Siri Agrell |
Aut Tyalie is Elvish for "Go Play Games"  Players Wanted: Burnsville/Eagan MN game, War of the Burning Sky campaign | 
And yet another word from our sponsors
