Like everyone else, Bob Cratchit and Fred are shocked and astonished at Scrooge's sudden transformation. They've always known him as an ornery old skinflint who hates Christmas. Yet now he's fully entered into the holiday spirit, spreading nothing but joy around him instead of gloom as he always used to. When Scrooge gives Bob Cratchit a generous raise, the underpaid, overworked clerk can't believe his own ears. Scrooge's generosity is so out of character that Bob thinks that his boss has taken leave of his senses. He even seriously considers calling for someone to bring a straightjacket.

As for Fred, Scrooge's nephew, he's both astonished and delighted to see old Ebenezer show up at his house for Christmas dinner. When Fred invited him earlier, Scrooge turned him down flat, making it abundantly clear that he thought Christmas was nothing but a load of old humbug. Yet here he is at Fred's door, almost begging to be let in. Fred bears his uncle no grudges and doesn't hesitate to invite him into the dining room.

I'm sorry, but we cannot write this for you -- what we can do is to give you some ideas that will help you do your own work.

Surely, the first reaction of Bob Cratchit and Fred will be astonishment.  You can talk about all the things that Scrooge has done in the past that would make this so amazing.  Talk about how, for example, Scrooge scolded Fred so harshly just for stopping by to say Merry Christmas.

Next, I would speculate a bit about why this has happened.  If someone you know changed so much so quickly, I would think that you would wonder how it could have happened.  So you should try to make some guesses (from their perspective) as to what could have changed Scrooge's personality so dramatically.