Red John is not one person, its a group of people organised as tight secret society. I would say 2-4 men/women, very intelligent and powerful, followed by network of powerful helpers/followers, very highly ranked society members, recruited because of their position, power or skills. Beneath them is group of soldiers, recruted and used when needed.
Within the top 2-4 there is a leader, Primus Inter Pares. Also there is a number of apprentices, trained and prepared to rise when their time comes.
One of the leaders, probably Primus, is someone that appears in Janes life from time to time, as he cannot withold attraction to Jane. Jane is obvious candidate for the apprentice, they want to turn him to the dark side. Killing his familly was part of the initiation process where they try to reboot him through a tragedy, separate him from anything he cares in this world so he can just step into darkness...
