I had an awesome run with a group of all 3rd level characters with a 4th level cleric in the Water Works quests on elite. I think we had one death by an ogre due to an unexpected heavy critical. We worked together, we communicated, things went smooth.
It sounds like the distinction between who was leader was vague in this group. Being you took it upon yourself to lead as you said, and the party was way ahead of you to the point of having HALF the party slain by the time you were loading part 3 tells me either you weren't leading or failed to take the lead which caused the party to wipe.
For some reason, they didn't see you as boss...and you couldn't catch up. For some reason you took the lead and then abandoned it, or did so half heartedly which in turn gave you the plausible result for this. Of course there would be confusion and chaos. THERE WERE NO LEADERS!!!! Even you went your own way. You seem to have thought you were the leader but somehow, somewhere down the line you were the one that was straggling behind. Too many chiefs not enough Indians I say, and I say this because the chief must also realize he is an Indian.
It takes a long time for oozes to kill three members of a party unless everyone froze up in lag. What were you doing this whole time...get lost on the way to tunnelworm? Was the group unaware you made a last ditch effort to shrine at the very last second having to go back a couple corridors?
You all failed...as a group. Not pointing fingers at anyone, just at some of the things I saw objectively in what you said. There are no faults only lessons to be learned. Those who never fail are those who never try.