Hm. Tried this 4 or 5 times and kept failing. For me, Crispin dies about round 6. Round 5 if there's a crit. Without the damage from 7, 8 & 9 the beetles just don't last long enough to take the dogs down. Maybe something changed.
Used a SS rabbit in first slot (flurry, dodge, burrow) and just weaved dodges with flurries. Maybe got lucky with malfunctions or RNG but rabbit finished off weaver and half of fire starter. Never had to bring in 3rd pet
3rd pet didn't even need to come in. I don't have a Fire Beetle but I do have 2 Lava Beetles so it would have been okay anyway. I think I Scorched Earth with my Destro Lava Beetle when 3rd enemy pet came in, then Cauterized before the enemy pet suicided.