attacking a fortified position

So I built a dungeon based on ruins in a jungle.  An evil warband...mostly Orcs headed by a handful of mercenaries. (levelled NPCs with a bunch of Orc thugs) Have found these ruins which have 2 healing fountains on them, and have found clues that the ruins might lead to a dungeon, but they haven't been able to find the door yet...The local militia...tired of the Mercenaries raiding local merchants have staked out a piece of the ruins and now need skilled PCs to force their way in and take out the well supplied mercenaries and their orc and monster henchman.

 the overview from the direction the PCs will enter.  The local militia with archers has managed to stay safe within the area that was once an entryway of some type.  However they are equally pinned down by orc archers.

 The PCs will have to move out cautiously and engage the enemy.

 It took Militia a while to find the Mercenary bandits, and they were fairly well settle, and very well supplied.

 The jungle has claimed large areas of whatever this structure once was

A side view....