Alright, gotcha. In that case I think Sarith should map and Orsik should take his place on rear guard, since mapping requires no check and Orsik's perception is better.
If that's ok with you, new roster (sans dead--RIP guys, *pours out a 40*) would be:
Pace Normal:
6 miles per day
Foraging: disadvantage
Stealth: disadvantage
Navigation: normal
Perception: normal
Pursuit: No change
Guarding:
Ezraen (Perception +2, Insight +2)
Lookouts:
Bertram (front) (Perception +6)
Orsik (rear) (Perception +3)
Navigation:
Surana (Survival +2)
Shuushar (Survival +4)
Foraging:
Derendil (Survival +1)
Topsy (Survival +0)
Turvy (Survival +0)
Covering Tracks:
Eldeth (Survival +5)
Mapping
Sarith (No check)
Marching order (inferred from tasking)
Front Rank:
Bertram
Surana
Shuushar
Middle/Main body:
Derendil
Topsy
Turvy
Sarith
Ezraen
Rear:
Orsik
Eldeth