Mr C and Richard
Mr C, evil as he is, is certainly capable of committing rape. But it seems "out of character" to have carried out the act on a comatose Audrey. Mr C and Bob especially I would think get off not on the act, but the terror and trauma imposed on others.. garmonbozia. So if he's the father, I'd bet it was after Audrey's "recovery." Being manipulated by Mr C, taken advantage of by someone she thought she was in love with.. then maybe learning the truth? This I can see wrecking her emotionally. Add in the demon seed son that would follow and her present psychological state is completely understandable.
I don't Mr. C was out to inflict terror on Audrey. I think he wanted to plant his seed, and raped Audrey while in her coma in order to do so. The clues to this have been given to us during the run of The Return, so I wouldn't look to complicate that aspect.
I don't even think it crossed his mind that he might impregnate her. He just saw her there and raped her.