Yep, though with calibre in particular you want to kind of make sure it's locked down real good. People sniff for the ports it uses, so open calibre-web libraries get found quickly, and then will usually have some attempts at cracking.

I had mine set up as a local-only thing (could only access from my home WiFi), but from experiences with other apps that have similar crawlers, it takes about a week for them to be found. Just make sure everyone's passwords are decent, or just share one account if it's people you trust.

Thats the idea! You just have to get them off the store and download them somehow.