I am certain that every one of the six inmates eventually made their way into the catacombs beneath the Asylum in order to escape unseen.  Though many of the events that occurred directly underneath the Asylum were obscured by the flooding, it actually was a blessing in disguise.  The water allowed me to see six distinctly different tracks.   Strangely, almost all of the inmates went separate directions.  According to the tracks, at least, I can definitively say that all of the barmies did not escape together.  They left in three different waves.  This distinction does not necessarily mean that the different "waves" left at the same time or even together--it just means that in order from first to last, they were the most interested in escaping. 

Eliath, Trolan, and Malazar all disappeared, with very little evidence to go on.  Though these three were part of the first "wave," I do not think they were necessarily together.  Eliath and Trolan initially left going the exact same direction at the same time.  There are also the tracks of a third, more furtive fugitive, who I believe to be The Oldest Barmy (purely by process of elimination).  These three apparently escaped going the same route.  At a crossroads, they all split off, going separate directions.  However, the Oldest Barmy began going one direction, waited, doubled back and went in the direction he had just come from!

The second "wave," which includes the Hound and the Oldest Barmy, is even more interesting.  As mentioned above, the Oldest Barmy initially went with Eliath and Trolan, but then doubled back as soon as they all split up.  I have tracked the Hound for some time now, so I can say with certainty that he began following the trail that I believe is Malazar's.  The Hound, very suddenly and quickly, also backtracked to the original cavern underneath the Asylum.  They both reached the flooded cavern at approximately the same time.  Eye-witness accounts can perhaps help to explain what happened next.

By this time, the entire Gatehouse had been alerted to the disappearances.  They had already found the tunnel in the Oldest Barmy's room and they were on their way to the catacombs beneath to apprehend them.  (Interesting side note: Captain Morgan recalls still seeing Lawshredder in his cell and "breathing a sigh of relief" when the other barmies were noticed missing)  Once the guards reached the flooded cavern below they saw the Oldest Barmy looking like he had just been in a scuffle, screaming and splashing helplessly through the water.  He supposedly fought off the guards for many minutes, always going back to one spot in the ground that he'd dig at until attacked.  The only thing he would scream was "He took my soul," and he'd say it over and over again.  Eventually, he snapped out of it and escaped somehow managing to elude his pursuers.  He fled the same direction that the Hound went after he backtracked.  

The third wave involved only Sougad Lawshredder.  I can also say with some certainty that Sougad Lawshredder was "following" at least one of the inmates.  He doubled back several times and his progress was very slow, as if he was more concerned with tracking, than escaping.  Though it is difficult to say anything for sure, if I had to make an educated guess, I would say that Sougad was following Malazar.