To address your claims of FileMakers lack of documentation and incompetence:
Do yourself a favor and please see these links!
Go to page 9 and see "Before you Begin"
Specifically the part that states "Ensure that no existing websites on the machine use port 80 or 443".
Furthermore you may want to review page 25 (See illustration)
Look here too: (See "Items to Verify")
Some helpful info here
https://fmhelp.filemaker.com/docs/13/en/fms13_help.pdf ( Page 260 ports used by FileMaker server)
You missed this as well?
So since you are having trouble due to "FileMakers negligence"
You should consider putting your install on dedicated machine or virtual machine. << This may be the least confusing way to use the Mortland Method
There is another way
This requires editing your server.app apache config files and your http.conf files. This method is not supported by FileMaker or Apple. It requires doing some research!…but is possible ....Good Luck!