@futurebird if it’s only intranet and only Macs, you might be able to get away with not doing anything for the domains thanks to Bonjour (self-assigned computer-name.local domain names, I use this regularly to test mobile web stuff running on my laptop).
Alternatively, you can configure a public domain to point to the internal IP, assuming it’s static (I also have this locally for services running on non-Macs.) if the domain/IPs must stay secret, it requires an internal DNS server as well.