First off, I very much appreciate the responses. A couple of quick clarifications:
The Aasimar twins together will have solid ranged options - battle dance + high dex + arcane strike + various other potential buffs do indeed add up. I just meant to say that we didn't have the sort of ranged threat that a dedicated archer or blaster-type might offer and wasn't sure if that would be a big detriment or not.
Skill-wise the way we're kind of looking at things is the Dervishes will have effectively maxed out Perception, Stealth, Acrobatics and (via Versatile Performance) Diplomacy, Sense Motive, Bluff and Intimidate, all fairly soon. They'll also have a touch of Knowledge: Religion and Escape Artist.
The Oracle will have Healing and a pretty diverse smattering of Knowledges while the Summoner will have Knowledge: Planes for certain.
Apart from trap-finding, what skills would we be lacking that the AP might require?
I'll look into the Player's Guide. Perhaps one twin would focus on Perception with Trap-Finding and the other on Disable Device? The two plan on serving as the 'scouts' of the group already.
EDIT: Shaman, I really appreciate the effort put into that lengthy and informative response, but the players are in love with the idea of playing identical builds intended to be complimentary. The Halfling player actually seriously considered running an Archeologist (with a dip in Halfling Opportunist) but felt that the group lacked any sort of legitimate 'tank' and has always wanted to run a Summoner type.