Here's two quick reads that might help -
$1https://quicklygoingblind.blogspot.com/2022/03/going-blind-is-hard-being-blind-is-easy.html
I've come to understand the only disability that holds people back is having a bad attitude. Everything else is just a speed bump. Your father can have a rewarding and happy life if he allows himself to accept his new reality.
It isn't easy. I grieved when I got the diagnosis. I grieved the loss of my sense of purpose more than the loss of my eyesight. And it took awhile to get my head straight again.
It's something that has to come from within. Unfortunately there isn't much anybody except your father can do. Acceptance is a choice only he can make.
But there are some ways to make it easier for him. Don't treat him any differently than you did when he could see. Make him feel needed. Ask his advice. Learn from his wisdom. His abilities have changed but his need to feel like a contributing member of the family hasn't. Find ways for him to contribute.
Good luck, and please let us know how the vacation goes.