First off, Red john cannot be a member of Jane's family; looking for personal vengeance against jane like his brother jimmy, cos red john started killing long before he knew Jane. kirkland and brett are being painted as red john possibilities by the producers and its way too obvious. They cant be. Personally, i think its Dr linus wagner, travel back to the first episode, check out the handshake scene between the dr and jane, it was a bit too epic. in the season 1 episode 'red johns friends', The man that patrick helped from prison, who later escaped to mexico where he met his waterloo in a bathub, he wrote on the wall, and i quote 'He is ma{r}{n} the last letter could be a 'r' or 'n' more likely 'r'. it could mean he is marooned, which means in a place he cant get out from {prison} this points to linus wagner. He could have his ways of getting out and returning, maybe through the laundry van like our thief friend in 'like a redheaded stepchild' in earlier season or have people do his dirty work from outside. In prison he could do a lot of research about patrick, resulting in his infinite knowledge about patrick. And i guess we all know that Red john calls the mentalist by the name 'patrick'  leaving most of the other suspects out of it.