Oh wow! My dad had hiccups after his surgery and it was excruciating for him! I'm so sorry your father is going through that. Unfortunately, we don't have any advice (just commiseration) on how to get rid of them. They just went away for my dad. He tried a hiccup syrup but gave up on it, as didn't see an improvement. He also tried all the "old wives tales", which I'm sure you've already looked into as well.
Would it help to just have your dad taking small, frequent sips of water, to slowly improve his hydration? I'm sure you've already thought about it all.
My dad initially regretted the decision to have the surgery, too. I still can't say that he's glad he had the surgery, but I think he's closer to that point. Did the support group help your dad? I know the family is trying to help but saying "you should be grateful" to someone who's gone through and is still recovering from such an intense surgery doesn't seem very helpful to me. Hopefully the people in the support group helped to validate his feelings and experiences.
How is your dad doing now? Tell him I'll be praying for his recovery so he can go fishing!
Sincerely,
MJ