Just a thought but are extended family involved???
I OFTEN have my Grandson for weekends etc to give my daughter a break and her sister occasionally has my Grandson too even with a little one of her own
I had him for 2 weeks recently while his Mum jetted off to Jamaica ... But I vaguely remember the words ''never again'' exiting my mouth while in a comatosed state by the end of it!
I love doing my bit though and Grandparents etc are important to children
Have a great bond with my Grandchildren and also took little man abroad with me on holiday which he loved and I genuinely loved every minute too & for me it's creating happy memories as well as giving parent/s a break
Even if you didn't end up doing things together you could veg out and watch some sports etc and Mum could have a hot soak in the bath and a SLEEP , both knowing kids were happily baking cakes or playing in the garden at Grandparents house , family is a team , and being a Nan or Granddad is an enjoyable role!
I don't know about palming them off to Dad for a break or his turn on a Saturday morning as I had to bring up my 2 girls on my own and rarely if ever got a break ( but not complaining , they turned out LOVELY! )