So what are you missing?
Parallels is a virtual machine software ie to run windows on a mac within a program window.
To setup multiple terminals you need to be using SQL Express;
Your linked post is about multiple congruent RDP sessions which is a whole different thing.
This refereed to a ‘HACK’ to allow multiple RDP sessions on a non RDP server copy of windows.
This patch has been fixed in a windows update and is both not reconmended as would require running non updated windows with updated disabled…
You wouldn’t run parallels on a mobile device, if it is a non windows device you would run RDP Remote Desktop which is a free windows app which remote controlls another machine.
The ‘Patch’ which is actually a HACK allows multiple RDP logins to a single PC (against Microsoft Terms).
In theory you should have a PC per RDP device or get a copy of Windows RDP Server.