need a private publisher for my book

[relayerbob]

11. It's complex

It would depend on whether the art is actually public domain or is owned by the estate of the artists, or someone else. And then, the Church may need to give permission, also. The fact that they are displaying the art, doesn't mean they own the copyright to it. Most likely they wouldn't. Similar to how my owning a CD doesn't give me any rights under copyright law, expect to make personal copies for myself only for archival purposes. I'm sure the book publisher knows that these things are complex and convoluted and the research alone would likely cost them more than they could ever hope to make off of your sale ... not counting any potential litigation. They can't take your word for it, because as someone else noted, they are the ones selling you the book, so they would be on the hook for it.

In any case, you might be better off incorporating it into a really good Word or PDF document and sending it out. While still not actually legal, since no money is changing hands, the worst you would likely get is a case-and-desist, assuming someone learned about it and cared enough to bother with doing that, which would be unlikely.