Man do I know what this is like.
There are no words for it, I've got nothing but tears for you. It's gonna be hard, but it's supposed to be. Just be there and hope he gets peace and rest soon. Not an easy thing, but I was there with my father until the end last December and I know exactly what you're going through. It's a hard position to be in, but there's a sense of beauty in the emotions you go through as well. The emotions you visit during times like this are very powerful, something I learned last year when I losy my father. Strange to find beauty in such a situation but it's overall an emotion towards life. Life is huge, bigger than any of us can even imagine. Hard to explain but I think those who have been there can understand what I'm trying to say. Nothing about it is easy but it's one of those things we all have to go through. I'm not a person of faith but since I lost my father I've been venturing into thoughts of spirituality that I never would have gone to if my father were still alive. Powerful stuff life is, as ugly and as tough it can be sometimes, there's always something to appreciate in it all. I'm sure you already are, but be thankful you have the awesome memories you have with him. For those memories will be what keeps your strength going after this hard time.
Wish the best to you and your family. Hang in there and stay strong.