2 BLU takes up extra spot which can be another 2h DD, and if you split spell you can't set DD trait, thus pt dmg output is lowered with 2 BLU.
No .. just no.

Both BLU's go into the mage pt with the 2 BLMs and Ninja. That leaves two slots for RNG / whatever you toss into it.

DD parties are

BRD
WHM
COR
DD (SAM / WAR / DRK / MNK / maybe RNG)
DD (SAM / WAR / DRK / MNK / maybe RNG)
DD (SAM / WAR / DRK / MNK / maybe RNG)

Try to have a DRK in each DD PT for enhanced chaos roll, otherwise try to have at least one of each of those jobs with RNG being a toss up depending on where your slots are and if their good or not.