The Priest
Wanderer
No
A champion spawn will only accept one such Virtuous Challenge per session. Only one person may affect a given champion spawn session, and only once during that session. Once a champion spawn’s level has been increased by a player, no one else can increase its level until the spawn has been completely defeated and has restarted.
I still play OSI, and this is wrong. You can pop both to start the spawn and advance the spawn one red candle. They also added a patch very recently so that the number of spawn per candle is decreased but you still have to kill the same number of mobs to advance the champ.