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What I assume is that the facility has the ability to cure otherwise incurable or fatal injuries/diseases, however, in doing so it turns the patient into an abomination.
As it was Red's hand that activated the video, this could be seen as evidence that Red was an employee, but on the other hand, Red was just as trapped as Ruby and Tom, as we saw by his suicide. It is possible he was an employee who later became a prisoner, possibly because of his crime against ruby. We can't yet know the motivation for Red's crime, nor whether he actually killed Ruby, or just injured her, and Ace marked her as being dead.
Ace is an interesting character. So far, his intentions seem good: due to his marking Ruby as deceased, and the note in the medical room that read "despite [Ace]'s best intentions..." we can conclude that he is a staff member, probably a doctor. Whether he is doing this because he genuinely wants to help, or because he wants to do crazy experiments, we do not know.
Stitches has recovered from being a bloody mass with little more than a spine and head. Now that he has recovered, he is still able to talk and has some kind of conscience, showing the power of the facility.
The Hound Zombie and F are probably the two other characters.