Mmmh, let me think.
Well, I believe I could 100% trust Frederick. He would most likely refuse the money altogether and let me handle it. At that point, I would give him some, because he's a pretty good guy. And still, I believe if he were to spend the money, he would most likely donate it to charity or for the sake of medical research. He would probably keep a small amount for himself to buy books.
Nigel, on the other hand, would certainly spend all of my money in food and other stuff for himself. Sometimes he can be a bit greedy and selfish, so I wouldn't be surprised if he spent everything.
As for Kay, well... I can't say much about him, since he's still a mysterious guy and not much is known about him, but based on how he has been so far, I believe he would spend the money in horses, books and for the sake of the poor.