I belive your M113 is carrying somebody... Why not set a condition to the Cond field of the waypoint "UNLOAD" (Not "TRANSPORT UNLOAD"!, as it's used when passengers are not of the same team of the M113), and the M113 shall wait until is has been satisfied:
Cond: !(Leader this in vehicle this)
Now, a question...
Your guys are in the same group of the M113, right?
Otherwise, you'd need to use a "TRANSPORT UNLOAD" type waypoint in order to unload the carried team (from another group).
If it still doesn't work, make a trigger at the unloading zone which "execs" a script that would deactivate the driver of the M113 (temporary) and unassign the vehicle foreach passenger:
@UnitReady MyM113
driver MyM113 stop true //You could try 'dostop' instead
"Unassignvehicle _x" foreach units group MyM113 - [driver MyM113, gunner MyM113]
@"_x in MyM113" count units group MyM113 - [driver MyM113, gunner MyM113]
driver MyM113 stop false
exit