The reading for 反 is all good. The reading for 省 is an on'yomi reading you haven't seen yet. Here's a mnemonic:
I'm standing in front of you, forcing a reconsideration of your anti conserve stance, with my saber (せい) to your throat. I better see some reflection on your face or you won't have one in a second.
I’ve been reflecting on it, so please don’t be so hard on me.