Originally Posted by DracoDei
Unfortunately, I think you may need to break it down by which skills are availible when which fiend is in command in the stat block for individual creatures.
It says in the entry that they use they skill modifier of all the fiends within them. That implied(though I should make it clearer) that they use the best modifier of all the skills that fiend has access too(if said skill is Int, Wis or Cha based). If a fiend has taken Dominion, that dominant fiend only uses their own skill ranks and the skills based on Str, Dex or Con of the host.