How do I set up Closed Membership

My site is primarily a site for my organization. While there are pages that are open to the public, there is content that I I only want available to the organization’s members. We have a closed membership are currently require dues are to be paid by check (we are not yet ready to collect dues through the website.)

If I add members in manually, is there any way to remove everything regarding registration or join us from the log in process or closed site pages? I don’t want to give anyone the option or idea that they can register and get access to the private pages.