I wouldnt approach it from the side of if you dont do ABC you wont get to see your grandson, do it the other way - it is so important for him to have you in his life and we want him to spend time with you - you need to be consistent with our parenting wishes etc...

It is important to have these people in your lives - even if nothing else but to give you a break occasionally - it is something I never get and would value very highly, and yes sometimes it does take a bit of compromise - but not to the point of endangering a bubs health of course..