This is the text for page 13.
She said we're over doing it
しかしだ変身するまえにちゃんと十分資料はあつめて研究したはずだろう。 フィルム 本 テープ などからくしんしてわり出したかっこうが。これなんだぞ。 どこもまちがっていないはずだ
However, before disguising ourselves, we did plenty of research. We waded through films, books, tapes and so on. What about that? I don't think we made any mistakes anywhere.
Sarge, let's off that creepy human bat!
"Taichou" is "commanding officer". There's no implied rank here, so it could be used for a leader of a squad, up to a regiment. I could use "Sarge" , "Lieutenant" or even "General". One source on the net claims that it's usually applied to Captains. But, this is a small scouting party, so it's a toss-up between "Sarge" and simply "Sir". I'm going to use "Sarge" until later corrected.
ばかっ 殺すとさわぎが大きくなって われわれの正体がばれてしまうぞっ
Idiot, killing her would cause a big uproar, and we'd be exposed for sure.
I'm taking some major license here. "This killing thing would big ruckus turn into" and "our true form exposed would do". It's implied that the killing would be directed at the old woman, and that the exposure of their true nature, which they're already describing, would naturally follow.
Ignore whatever that old bat says. We're keeping with the escaped prisoner cover.
One interesting thing (yes, I know that there are may interesting things) about Japanese is its ability to turn virtually any word into a name for someone. In this case, "oibore", which is a noun meaning "senile old fool" is used to directly refer to the old woman.
"ha" is a shortened form of "hai" in this case.
I told you to call me "aniki"!