Our group has an inquisitor, a witch, a sorcerer, a bard/ranger, and a barbarian. What class would actually serve a purpose without taking the spotlight off of someone else?
Cleric/oracle would seem to be the biggest need. Trap finding would also be quite useful for that group.
A divine spellcaster looks like it would be useful to that group.. so cleric/oracle/druid imo. Trapfinding is always useful as Gerald said, but healing through any traps also works. :P
Our group has an inquisitor, a witch, a sorcerer, a bard/ranger, and a barbarian. What class would actually serve a purpose without taking the spotlight off of someone else?
What type of Witch, Sorcerer, Inquisitor, Bard? What those characters are built like will go a long way in determining what you need.
I suggest that the bard/ranger take the Trapper archetype. It gives Trapfinding and Disable Device at level one, but doesn't give anything up except spells. But, in a multiclass build, you're not likely to get any useful Ranger spells anyway:)
Now that traps are covered, a full divine caster sounds like the only thing the party might be "missing".
I recently started playing a cleric in PFS. I hadn't played one in decades, and I'm surprised how fun it is. He's a lot more than a walking band aid, but he can do that, too.
Not a lot of skills, but it looks like your group has that pretty well covered.