Mac mini-hosted WordPress websites won’t load on any of the Macs on LAN

I have three Mac minis on our LAN, all of which have Yosemite and OS X Server, but only one is enabled as a web server. My problem is that I can see the WordPress-based websites hosted on this web server externally, and on all the Windows machines on our LAN, but not on ANY of the Macs on our LAN.

One of our company's most important applications is based on being able to have one of the Macs query the webserver with http_get from time to time, and lately this query gets timedout or rejected also.

Pic of our LAN

All of the websites used to be view-able in Safari on the Macs, but sometime in the last few months they quit loading. The only really big change we've had is the installation of a new router (a Mikrotik that's a little tough to navigate). Here's what I've tried so far:

• Scanned the web server for malware and viruses, nothing bad reported, no website proxy changes, etc.
• Removed all cookies, etc. from Safari and reloaded website, no luck
• Installed Chrome to see if it was just a Safari problem, same errors but slightly different message ("ERR_EMPTY_RESPONSE")
• Checked to see that the router/DNS entries in networking settings of the Macs were configured well to the new Mikrotik (but again, not an expert on the Mikrotik end)
• OS X Server Websites dashboard says that all websites are available on local network (green dashboard lights)
• The webserver's default website (with the cute "Welcome" pic) IS accessible.
• Checked the permissions on the website folders to ensure that _www permissions are good, etc. (again the WordPress websites work externally but not internally on just Mac machines, except for the OS X default website)
• Checked apache access and error logs on the web server. Nothing showing up there – the attempt to access the website isn't even listed.

My guess is that there is something about the new Mikrotik router that is not allowing the Macs (based on how they're all configured) to see the locally hosted websites. But it could be a variety of other things too… I'd really appreciate any help.