Ghoul Swarm
All the ghouls in the crypts will attempt to swarm the player characters, in either the Upper Chamber or the Lower Chamber - whichever they enter first. This can only be avoided if the players are stealthy enough to systematically and silently eliminate the ghouls without awareness of their presence propagating to the others.
The assumption is that there are 13 ghouls, but it is possible there are more and that the players have permitted some to escape the village - in which case, the additional ghouls should be distributed evenly between the two prongs of the attack.
Tactics
In most situations, when the players enter into either the Upper Chamber or Lower Chamber, all of the remaining ghouls will rush from where they have moved in behind them to the Middle Chamber, and from the Last Chamber in front of them, normally this will be seven charging in from the Middle Chamber and six charging in from the Final Chamber.
The ghouls will focus first on grappling, with two or more ghouls attempting to grapple the more heavily armed and armoured player characters so that other ghouls can attack them while they are helpless. Extra ghouls will divide themselves somewhat randomly among the remaining weaker players as possible.
During the battle, the players will notice that all of the ghouls look like the ordinary villagers od Cosutanu, except for one - this one is (or used to be) an avian woman, and is wearing gear more appropriate to an adventurer. This ghoul is an important piece of evidence: the remains of Lorienza Lioni.