This is how I've always done BD C runs:

First thing's first: Group your team. Group as follows:

-DPS group-your two party members who deal the most damage.
-Non-DPS group-your two party members who deal the least damage.
-Bruce group-the person with Bruce.

When the mission starts, have the DPS group go left with Bruce group. When the non-DPS group unlocks the first door, you'll be able to flatten the next room in no time.

When you beat the first dark room, have Bruce group go it alone to the portals. Bruce will (YES, HE WILL) tell you the portal:

-"Pistol skills": Left
-"One-handed sword": Right
-"Only one answer": Forward
-Anything Else: Back

Bruce can go it alone, because it's only three vandas. >>

As for the key, whoever gets there first can pick it up. The rest continue on.

Have your Ranger split from you here to go through the gates to kill the vandas and get the key.

The rest should be doing the following:

-Person who's best with the switches guiding the Ranger.
-One person should be killing the Lapuchas that spawn.
-The rest should be at the door.

For block 2:

Have the DPS group go right. They'll catch up. Have the non-DPS group go with Bruce, left. Have one of those people (any really) stay at the door to kill the Vandas.

When it comes to the turn near the end, have the highest damage dealer go right and the rest go left. (Person 2 from the DPS groups goes with you)

This should yield good results, it's done so for me.