It's a big party, with a Summoner, the choice is already made for you:
Bard/Skald... Or Evangelist Cleric...
Race: any
*human*
Trait:
Memorable
1. *Arcane Strike*
1. Combat Reflexes
3. Bodyguard
5. Extra Performance
7. Flagbearer
9. Master Performer
11. Discordant Voice
13. Grandmaster Performer
Gear of interest: +1 Impervious Whipwood Longspear, Banner of Ancient Kings, Dervish Sikke, *Gloves of Arcane Striking*
Arcane Strike, with the Gloves of Arcane Striking is almost worth going Bard/Skald over Evangelist Cleric... but the Cleric gets Divine Interference...
Another option is the Sensei-Qinggong-Monk of the Four Winds.
This plays a little differently than your typical Bard/Skald or Evangelist Cleric, but is handing out much of the same Performance stuffs. Monk of the Four winds has a Slow Time ability at level 12, and Sensei's Mystic Wisdom allows it to hand out abilities to allies...
Giving out a bunch of extra standard actions to a big party full of summoned creatures can be interesting, to say the least. They can't be used for spells, but Vital Strike and Grapple immediately come to mind. Use it to ready an attack to even further break action economy. Free round of Aid Another for everyone...
Ranged damage: well and truly covered.
Healing: also covered.
Melee: 2 is probably enough but there's probably room for another if that's what you want.
Buffs: an oracle and a summoner are enough, but you could do another means...but there again it's hardly necessary.
Debuffs and battlefield control: possibly a sideline of the alchemists and the inquisitor may scare people a little but that's about it.
So I'd do battlefield control primarily, whether by spell or by combat maneuver. A grappler, a druid, or a winter witch could do this for example, each in their different ways.
If 3rd party is available that opens up options in that line, but I'm not sure I'd take them if everyone else is going pure Paizo.
If the third group is accessible then I recommend the tactician or the vitalist, both give a lot for the team since by placing them in their group you can apply powers and abilities without having to resort to mobility on the battlefield
Telepathy: both classes earn it so that the members within the collective will be able to pass on any information without revealing anything to their enemy, this works even better if you have collective enlargement.since being captured By the enemy, Go exploring or in other circumstances may pass information and be prepared for any circumstance.
Tactician: Good for improvising skills on the battlefield by bestowing strategy and teamwork feats on party members
Vitalist: It is good to heal and buffer team members if they are within their collective and without the need to touch them (highly recommended on my part)
If you have very low primary attributes to add members to your collective, I recommend using expanded collective, this will add 2 more members and can be taken multiple times.
I would second avr that the biggest need is likely to be battlefield control and de-buffing.
A witch is probably the best de-buffing class and, if you select a variety of spells, can be decent or better at other roles (either to augment other PCs or fill in gaps) when needed.
If you want to mix combat and de-buffing, then mesmerist (specifically, inspired blade swashbuckler 1/vexing daredevil mesmerist to qualify for Fencing Grace at 1st level) may make a good partner for the oracle.
Alternately, you could go with druid. You can focus on battlefield control and/or blasting with spells and join in on combat with an animal companion and wild shape.