Just to give a quick update, thank you for those of you that were kind and helpful comments. First off, I agree with travel insurance and do purchase it for my family, I was in no way thinking that Carnival had any obligation to let them move the credit. My question was specifically for anyone that has encountered something similar and if they had any luck.
My brother is still numb on his left side having a little bit of a time walking, but his speech is good. He really wants to go and did not want to disappoint his family so he is planning on going, he will just bring his walker and go at his own pace.