Moses,
You will never change him and neither should you as this is what "he" is all about...my Dad was the same and I lost him when he was only 71 - bloody unfair!
Getting Grandson and Grandpa together is the most wonderful thing - you'll have to hang on the fringes though. What your son can learn about LIFE from your Dad no-one else can teach him and your father will love spending the time with his grandson.
I watched this happen with Dad and our eldest son who is now 14 (Dad died almost 4 years ago)...we parents took a step back and gave space for a truly beautiful relationship to flourish. This is more important than your Dad having some help to do the things he wants to do. It's the sharing with someone he loves that's important. You've had that with your Dad from the sound of it - and your son will be lucky enough to have that too
.