I think being the Taid is deep down inside of you mate and when you stop to really take it in you may find peace in that fact. My in law is a very long story in all honesty! but i can see that the little bit of time he take sout to be a grandad makes him happier than he may be for the rest of the day. He probably feels a lot like yourself in that regard but doesn't talk about it to anyone.
Forget about the big world out there and find your peace in where you keep it. Can't talk about zen and ying and yang and all that but the hardest and most rewarding thing to do when you feel like that is to find it and let the big world turn around that.
On the basis of not knowing you or anyhting you are/have been through i would say sometimes you dont need to combine the two sides of you if the worlds do not need to clash at any point. some people can seperate themselves from who they are and who they want to be, and some seperate themselves into different lives. If you feel that it is difficult to combine the two, perhaps take stock in where you could draw the line in the two worlds.
all i ask from my inlaw when it comes to being the taid is to simply enjoy his grandkids company, make them happy from them to be around. If you achieve that then most of the battle as the taid is already won. You put a smile on their faces and you are already their favourite person in the world. Everyhting else can fall in line after that.
Hope none of that sounds patronising mate, just trying to think out loud in regards to your thoughts. thats why half the explanations i type dont make sense, just type whats in my head and hope it comes out the same lol