I think there's still a misunderstanding here. Fay just said she didn't need up-front pay, and would agree to help the man without it, so the 200 gold the man paid up-front would be split between the other three instead of all four of them. (66 each instead of 50 each)

After the job is done, since the three of them got paid 2/3rds of their final 100 gold share, they would only get the remaining 1/3rd, while Fay would get the whole 100 gold share at the end of the job. She would not be paid more.