I'm not sure what you're trying to acheive here. Is it that the sky is too bright in the original and you want to tone it down?
Guessing that's it can I suggest this...
Take pic A exposed for the church.
Take pic B exposed for the Sky.
Put B in a seperate layer over A.
Add a mask to B and select it.
Paint Black onto the mask to reveal layer A below, if you make a mistake paint white on to the mask to correct it.