Hello!
I’m having issues installing UE4 as well. I have the Epic Games app, have clicked on “install Engine”, but it keeps telling me I am out of space. It says I have only 22GB free out of the 28 needed which isn’t true, I have 53GB!
I turned my computer on and off, uninstalled Epic Games and reinstalled it, signed in an out, nothing works. Any idea where the problem is?
Thanks for your time 
EDIT: finally solved my issue. Found out a big part of my free space was “purgeable” so I had to create huge files with a terminal until my computer told me my “disk is critically low”, and then deleted all files to purge all the memory.