Kathy Bates has 3 sons, all many years apart. You have a young child, teen, and an adult (who has his own family, Kathy despises her sons wife, played by Lady Gaga/Sarah Paulson, they're the protagonist and ultimately want to end this colt, leave and bring everybody to sanity) Kathy deserves a love interest.
Possibly Dr. Arden could return as Kathy's husband.
(Kathy's youngest son)
Angela Bassett runs the colt, she is the headmistress, the "queen b type" but little do we know she is answering to Papa Legba. Who we only hear the people in this colt talk about, they have never seen him, therefor they see him as a godly spirit, when in fact they're worshiping evil. This could remain, or we could see Angeal's character interact with Papa Legba depending on whether or not they can get the same actor back. I don't know the time differences, but maybe Angela could actually go back to playing Marie Laveau, because I believe she was around in like the 1800's? Not sure.
Jessica can return, or not it's open-ended. If she returns her look needs to completely transformed, I believe she should have black hair, like how she looked in her recent film "In Secret"
I see her running something, whether it's like a general store type thing, in a nearby area, or within the colt, but she tells things like they are. She has no time for ********, but maybe people don't listen to her, besides Gaga's/Sarah Paulsons character, who ultimately work together to take down the colt, the only reason they interact with this character is because they have too if they want their general supplies, this could be like when someone from the colt leaves the area, goes outside of the walls, and they view her character, Jessica Lange as insane, but in truth she is speaking the truth, she could be a godly woman who preaches from the bible. And tries to make them see the light. Possibly Gaga/Sarah's character is originally brainwashed, but after meeting Jessica's character starts to realize, after seeing how different it is outside the walls. And that is why Kathy's character eventually hates her sons wife.
Kathy's youngest son, also goes outside the walls on an occasion (and maybe he gets captured outside, but even possibly inside the walls, and we are meant to believe he went missing outside the walls, when in reality someone inside the walls has betrayed Kathy to take her child, maybe to bring them to good, before it's to late, the youngest is still learning so much about the world, and is still an innocent, and somehow ends up getting captured, I would say we don't know who it is, maybe eventually being revealed that it was Jessica's or even Gaga/Sarah's character, but her son goes missing for a while, and Kathy is so broken.
(This is where my concept began to run dry)
Literally anyone could play Jessica's character, someone new, someone old. Frances possibly, I don't see Lily playing it. I see Lily as someone so innocent, so brained washed, so far down drinking the kool aid, she is like the spokesperson for this colt.
Matt Bomer and Wes can stay on the outs, I don't need them to be filled with a ton of dialog, and screen time, they could be like local sheriffs in the small town, one maybe a little less brighter than the other. Cheyenne/Finn Wittrock could play Kathy's oldest son. And or Matt and Cheyanne could play sheriffs whilst Wes is like the higher up sheriff and Finn plays Kathy's son.
Emma Roberts I see her as someone who is consumed by learning, she reads lots of books, she is within the walls, she doesn't play a bitch, more on the innocent side, and can be turned around. Maybe even to the point where she doesn't speak whatsoever, and her character is silent, she must write what she wishes to say, which eventually she will speak up, for reasons of good, and hopefully helping a character in a terrible situation, to save their life. She also may ultimately sacrifice her life for the greater good.
Evan Peters I see as having like a disability, possibly down syndrome, something along those lines, it could just be Evan and his father (played by Denis O'Hare), he reverted to this colt because he felt like he had nowhere else to go. Denis O'Hare is possibly a farmer, and has relations with Jessica's character, he supplies goods to the general store.
Chloe (if she returns) should play a truly evil character, I want to see her go bat **** crazy.
wait... I still haven't got to read your script sis! 
