Do you want the church members to be able to add themselves to the list, or are you going to manage the member list?
It sounds like you are going to manage the member list in the database anyways. If that is the case, I would probably opt for a database security schema rather than using HTTP auth. If you go with HTTP auth, you will have to manage 2 lists of church members, 1 in the database and 1 in your .htaccess files. This always turns out to be a hassle.
If this is just a name & address type listing, how secure does it need to be? You might want to make a common sign on name/password and distribute it to all your church members. If you are planning more features in the future for this website, I would still go with the database security option.