Maybe the family gatherings are just that- the whole family gatherings. Why not arrange this so you can do-the-rounds for having an afternoon/ day/meal with just the one 'brood' rather than the full crew. Then there's more personal 'you' time from their children to you. Is it all hiking, rock climbing, a sailing etc ? How about Art &/or Music ? What's the grandchildren's favourite school subjects .... surely not simply sport ? There are pastimes other than those of the 'keep fit' brigades. What about Nature Walks ? Bird Watching ?
A famous matador gored by bull!
Sewing on Girl Guide badges, aaargh!!
