They were seeing these things for the first time, even they knew about it.

英訳に間違いが有れば正してください。

たとえ彼らがそのことに関しては知っていたとしても、初めて目の当たりにしていた。
They were seeing these things for the first time, even they knew about it.

ヒント
としても

答え evenをeven ifにする

They were seeing these things for the first time, even if they knew about it.

evenだけだと
~さえも、~すら、という意味

Even a child can do it.
子どもでもそれくらいのことはやれる。