This is offered gently to @CatLoaf and sharing to others...
As a mother (to adult dc) and a MIL, I find so many of these things difficult to navigate.
I love my dgc, I love having some time to care for them and I feel very happy to help out my dcs and dcs-in-law given the astronomical costs of child care. I have good relationships with all dcs and dcs-in-law (as far as I am aware and conscious that I can be a pita at times ), I feel priveleged to have such special time with dgc and happy that I'm trusted to be be an important part of their growing up.
There are SO many things that have changed over the years since I was a child (smacked by any adult in charge, travelled on someone's knee in the front seat of a car) and since my dc were young - slept on their side or front, weaned onto baby rice at 3months (2 months if they were a 'hungry' baby), use of CIO for sleep training...
With dcs and dcs-in-law I have always followed what they did whenever I could. However, sometimes it is difficult to understand exactly what the priorities are particularly when the priorities are different between different family members
"we don't generally let them watch cartoons but we don't mind if you do it occasionally"
"we don't usually let them have fast food but if you took them to McD's once in a blue moon, we wouldn't mind"
"we'd prefer if they didn't have a sleep late in the afternoon, but understand if that sometimes happens"
So then when information comes that is "we've stopped using the dummy" or "they need to use their words" or "the blankie is only for nighttimes" or "no fruit until they've tried everything on their plate". It can be difficult to know which developmental changes are all or nothing, and which ones are OK to adapt in particular circumstances, and again particularly when priorities and rules vary between different family members
And as a mid-60s grandparent, I find the most heartbreaking and deeply-exhausting times are when there is a dgc desperate for sleep, perhaps in their despair missing a mum/dad, and I'm denying them of both forms of familiar comfort. It feels cruel. And at my age that exhaustion brings me to my knees to I don't have the energy I used to to divert, redirect, entertain.
In general, I always follow dcs advice on anything related to safety. I prioritise anything related to food and health. I try to be an active and engaged gp and to minimise screen time wet January afternoons are an exception . I listen to parental information about changes to routines/habits/behaviour but please forgive me if I sometimes give in and don't get it right, all the time.
Also, to add to parts of the debate - my 2 year old undestood different rules at granny's house (what she could / couldn't touch) vis-a-vis Grandma's house.