Re: 2 User Licenses will not allow us to install and use 2nd license
You can use iCloud and so on in 2019 in the round robin fashion I describe above. For true multiuser where people are entering data at the same time on multiple machines the QuickBooks Mac Server requires that the machines be on the same subnet. The subnet is all the sections of the IP address except the last section (which identifies the individual computer/machine).
You can set up a Wide area network to have the same subnet. One way is using LogMeIn Hamachi as described in the QBLittleSquare article.
In any of these cases you can have the file in an iCloud shared folder. However it isn't a good idea to have multiple machines sharing the same file on an iCloud shared folder while that file is being shared by QuickBooks Mac Server.
Its all rather complicated but I'm trying to be accurate. If you relax the accuracy its easier to explain.