Some critics to your list.
Ryan O'Reily - ENTP One of the harder characters to type.. The persona is EXTPish.. always looking out for leverages and ways of self-gain, but he gives off a ISTP vibe.
Chris Keller -ENTP Disagree about the N.. he is a prime example of a ESTP manipulator.. he doesn't have any long-term goals.. and his motivations are usually erratic and more in terms of "Because i can". He enjoys manipulation and interact's tactically.. he is also engages physically and detail oriented. Changing the knife prop in the series final to the real one.. calling in favor with a friend to destroy the aryan brotherhood with anthrax... getting caught after robbing a store and escaping with a motorbike.. seems like ESTP things to do
Chris Keller, like Trinity said, could very well be caught in a Se loop to escape certain realities that his naturally inclined "Ne" would reveal. One time I clearly seem to get the impression of him as Ne is after he took the bullet for Tobey in the earlier season.
And, there's a scene when he finally returned from the hospital back to sharing the pod with Beecher, and Beecher wakes to find Chris huddled on the ground, rocking back and forth.
He spoke of, 'dying, being to hell and back, that he was there, but, they brought him back, to pay the penance'. He thinks of the big-picture, long-range, but, mostly in scams, which we don't see much 'abstraction' in. Ti?
But, his few insights into introspections (even with Sister Pete), we really saw him reaching (and reconciling) with 'what ifs'/possibilities/Ne. It's one he fears, even though its there naturally as his dominant function - we only see it's utility in schemes, ponzis, there's that N-flair/twist. But, true insight into his Ne-dom, in terms of abstract way of how the character viewed life, I think was skewed by the very reality of such a character 'getting caught and imprisoned'...thus, Se crutch to escape/ignore.
Ryan O'Reiley has this need to be the behind-the-scenes puppeteer of the whole Oz show....while he's backstage, snickering. This shows a want to interact (even if to manipulate), using
humans as pieces....thus, I'd make the case for extraversion (versus ISTP).
I think more than Keller, O'Reiley gives off a more S vibe, so I'm not entirely convinced on his N/S. I think if I tried hard enough I could probably argue a case for either, or. So, with any amount of confidence, I'd stick with: EXTP, as you've outlined.
His brother Cyril is obviously stunted, mental growth wise, but, I can see him being IXFP, which can work with the EXTP and IXFP dynamics, in terms of the extravert thinker 'tucking in the' introverted feeler under his wing, from the big bad world, if a level of care is already established (which, as brothers, they have).