Erratic and reckless = unpredictable and fearless though, which won't necessarily work in our favour. Craziness is a double-edged sword, but a sword nevertheless.
We don't have proof that they're inexperienced though. I mean, the lighter and the chanting is a strong indicator, but that could just as easily be a one-off miscalculation (not being familiar enough with our particular kind of monster, or the trick having worked beforehand), them being fed bad information by a usually trusted source, or worse, them simply being that desensitized to the idea of facing down a monster that the danger involved in blatantly walking up to one and attempting to kill it doesn't faze them at all. It's telling how they're the only humans (bar Taylor) who see us for what we are and are immediately committed to ending the threat; this suggests that there have been monsters in their lives before. What I'm saying is that the twins are a mystery to us, ultimately, just as we are to them.
They may not have much credibility, but if the MC takes that view, that gives them an advantage.
I'm not trying to invalidate your argument or change your mind btw - I just enjoy the discussion.