It’s fixed! This morning I noticed while looking at the log that our NAS is named “hooper.com” and that the pfSense firewall is also named “hooper.com”. So I changed the hostname from pfsense to pfsense_host and the domain from “hooper.com” to “hooper_firewall.com” (in System | General Setup). After these two simple changes I can reach the site from all of our computers.
I don’t understand why this fixed it, but I’m happy (and satisfied) that it did. Thanks to @atw and @cfoster for their efforts and I apologize for any time wasting that I caused.