The Basic strategy used in this level is to blow up the attacking myrks and ghols with the dorf mortars without using melee units.  The myrks are fiercesome in close combat, the melee should avoid engaging them.  Instead the trow should get the myrks to chase them down below the ramp.  The mortars set themselves up on the upper ramp outside the walls and rain death down on the myrks. 

Specifics:
               In the beginning the zerks should stay behind the dorf as much as they can.  This avoids a lot of trouble.  The dorf should target the incoming myrks by CTRL-CLICKing on the ground 15 ft in front of the myrks as they run towards him.  The dorf should only target myrks that are at least 20 ft away.  Don't do any short-range shots dorf!  Some of the shots you fire can fall short or long.  
If a mortar round falls short when you're already shooting a short range shot it's bad times.  The zerks and dorfs should be very conscious of each other.  The dorf should be looking to avoid shooting anywhere near the zerks.  By the same token, zerks should have a healthy respect for the destructive capacity of the dorfs.  This means that the zerks should be careful not to get in front of the dorf.  You never know when that little guy is gonna kneel down and put a round into the side of your head!  So as the game begins, the dorf should target only myrks that are well away from the zerks.  The zerks can help the situation by staying behind the dorf.  It's hard for the dorf to accidently frag you if you're behind him!  In fact, all units should try to stay 10 ft away from the dorfs at all times.  Again, the dorf should be conservative.  If the myrks are anywhere near the zerks you should hold your fire.  If need be, the zerks can kill all of the myrks that come at the beginning of the game without your help.  So don't feel like you have to soften up every single myrk.  Once reinforcements arrive, the trow should jump right in and kick those myrks.  Once that's accomplished, the trow and zerks should head outside without delay.  The trow should split up once they exit the city.  One goes south and the other north.  The trow should pretend they're in race to see who can get down off the ramp and onto the plain.  The dorfs should move towards the exit as soon as the trow kill all the myrks.  Don't put the dorfs on the tops of the towers.  They aren't very effective up there because they can't depress their mortars that far down.  The heron should stay inside until we know which way the enemy is coming from.  If the enemy is coming from the north, then the heron should stay inside, behind the dorfs.  One trow and the zerks should head south.  The other should go down the north ramp.  If the wave of myrks is coming from the north, they will ignore the northern trow if he doesn't get right it their path.  Instead they will chase after the trow and zerks that went south.  They'll go right past the center exit to the city.  The dorfs should set up right here in the exit and bomb the myrks as they pass by.  After they pass out of range of the dorfs, they should be weak enough for the trow and zerks to handle.  Again, the trow should get down on the lower plains asap.  From there they get the myrks to follow them around, back and forth in front of the upper ramp.  One trow will be responsible for the north, and the other will be responsible for the south.  The trow should go back and forth in a loop, not run in circles.  It's hard for the dorfs to predict the trow's path when they're running in circles.  Try to keep the trow's path nice and straight and predictable.  The dorfs and archers should now get outside the city and bomb the parade of myrks that is following the trow.  The heron should be hanging around behind the dorfs, being careful not to get in the dorfs' way.  The heron are there to take out any myrks that slip past the trow.  They can also whack some ghols too.  The heron should be on the lookout for roots lying on the ground from their fallen comrades.  Once they get these roots they should actually heal people too.  The trow can be healed, but only when they are more red than they are green.  It does no good to heal a fairly healthy trow.  If a trow turns to stone, you can de-petrify him by healing him.  This will only unfreeze him, he will need another heal to get him back into fighting form.  The zerks should be doing pretty much the same thing as the heron.  They're just there to protect the dorfs and maybe hack up a few ghols.
Red loops are the paths that trow should follow when the myrks are following them.
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