We need to deal as much a damage possible. If I firebomb leader and wolves after Cat casts the fog only Yulya can range attack. If the summons go in there and tackle the goblins 4 vs 3 they risk getting overwhelmed.

Does the fog stay in place or does it follow Cat? It would be best to stay at the entrance in the fog and attack anything that comes out. Let the summons ready their attacks and go at everything that comes into the fog. Otherwise we should range attack for a few rounds instead of going in there. The fire will do damage several rounds.