Easy fix, don’t go trying to use a game engine to do the job that a dedicated rendering pipeline should be doing…
Nevermind you the fact that epic wants to market to cinematrographers… its the same company that was well aware of eventual monetary repercussions to setting Screensaver that make you buy stuff on accident on fortnite, or openly ignoring california laws for parental consent etc.
Missleading is epic’s A game 
Arnold, V-ray, probably RenderMan (haven’t persoanlly used the last one, but I mean… pixar makes movies, I doubt there isnt an option to use cpu/gpu hibrid AND a farm/swarm on their main rendering tool…)
That said, maybe epic will some-day get their act together… more likely they go broke over another FCC or Apple sword though…
If you want to use quixel stuff, pay for the license, before they make it so you can’t 
Ps: fun fact, internally the picture rendering splits the image up for rendering in different batches that could be processed on anything else with the same scene installed/editor running.
For screenshots at least…