Fitech answered very quickly to email I sent them. Their official stance is the 2nd picture:
"On the duel quad system for plumbing the fuel lines. You can bring the feed line in to the rear throttle body and tee off to the front throttle to supply it. Then for the return line you can return off just the rear throttle body as it will set the fuel pressure. Then you can block off the return on the front throttle body."
However I might still do the 4th, passing the unregulated fuel pressure through the first one and using the 2nd one as the regulator. That way there won't be any dead ends where fuel might vaporize after shutting the car down when hot. Should be fine if it's also ok to plug the 2nd in without any return line.