Victory will be hard-won, if possible at all, as the enemies will have the advantage and be able to kill us one by one.
and after killing the son, prove that he was really doing something bad
2) We strike preemptively and cast a fire rune. This is the worst option, because it could lead to scenario B, and even in scenario A, most of the evidence of the son's criminal activity will likely be destroyed.
3) We just leave. And here I don't see any scenarios where something could go wrong. Before this, Ples and Revan specifically clarified that checking the mine is not part of our duties - no one will blame us for skipping it. Will the son steal the Grail or something else from the heart of the forest? Well, that's the security's fault, but not ours, because we patrolled the forest area properly, as specified in the contract. What else could happen? Will the Countess be killed? Well, we might still get paid a formal amount for the patrol and be let go in peace. Will we be called to defend the heart of the forest, and the battle there will be more difficult? It will be difficult anyway, and it's not certain that a more difficult battle can be created than the one where we move in a line through a narrow tunnel. At first, I suggested reporting what we saw, but now even that seems unnecessary - we might even be thrown in jail for slandering a respected person. Moreover, only the most observant saw it, that is, not even all members of the squad.