Depends what you need and how many friends you have. The following I am 100% sure can be obtained with 6 people or less:
Legs (Orobon):
Stone of Balance BLM BLU NIN PUP WAR
Jewel of Balance BST MNK RNG SAM SCH
Head (Corse + Wamoura):
Stone of Vision BRD RNG THF WAR WHM
Jewel of Vision COR MNK PUP RDM SAM
Card of Vision BLU DNC DRG PLD SCH
Feet (Dvergr+Walrus):
Jewel of Voyage BRD PUP SAM THF WHM
Coin of Voyage BLU COR DRK MNK SCH
Stone of Voyage DNC PLD RDM SMN WAR
I've heard the Amphiptere is doable with 6, though never personally fought him. The Taurus is a huge bitch, the Sandworm sucks too. I've never fought any T3 VNMs, Amphiptere, or Bugard. If you can't get 6 people, no clue what to say, some of the above can be done with 3-4 I'm pretty sure (Orobon and Dvergr for sure).