Assuming the list is real then RJ could not be a one person.

In Behind The Red Curtain. Kirkland asked Jason Lennon if he recognized him. And then kill him.
In Red Letter Day, Kirkland makes two other Homeland Agents break into Jane's roof at CBI so they can gather all of Jane's insights on the Red John case. Then he take it for himself and never report it.

If the list is not real.
We see that Bob Kirkland and Gale Bertram have secrets together.
In Black-Winged Redbird after Jane walk out of the Bertram office there is shown that Reede Smith, Thomas McAllister, and Gale Bertram share similar secret like Kirkland and Bertram before.
If they are not the killer then 4 peoples from that list cooperate to catch RJ.
So we left with Bret Stilles and Ray Haffner.
If the description given of Red John from Rosalinde Harker is true. Then Haffner is the only middle aged and healthy guy on the list. He admit that he was in Visualize and could bo on farm where Red John mark appear for the first time.