This will cause a hoo ha !

Don't smack
Perhaps they don't have all their usual toys to play with.
If weather permits, throw them out in the garden with a ball (get rid of some of their energy)

Your house, your rules!
If they run riot through the house, just say 'that's not what we do here'. If they take food into the sitting room, say 'no food in the sitting room, in this house we eat in the kitchen/dining room/wherever you eat' etc. 'We take our shoes off in this house and we don't jump all over the furniture' 'nor do we crayon on the walls'


Easier said than done.
I will let you know next week how I got on with mine (not all of them DGC)

For what it is worth (and I have my helmet securely in place and am hiding behind the parapet) I think a gentle smack is sometimes the best solution. I understand that the OP would never administer it, but feels it might help. I agree. I have to say that i have brought up three children using an occasional smack and as a result it has been that. An occasional smack. My children have always known the limits and respected them as a result.
There is a fine line between a light tap and leaving bruises.

My parents once stood over me debating whether I deserved to be smacked or whether my brother did! - needless to say I received the wallop!

It is so hard for grandparents when they have to stand back and watch ineffective discipline - but I have to remind myself that I did not always get it right, far from it.

I should have explained that I would not lay a finger on them my DS and DinL know that, but sometimes their behaviour is so naughty it is hard to know how to calm them down.

I really do not feel it harmed me to get an occasional smack, but nowadays I know it is illegal.

A smack is not 'a quick bit of a non violent reprimand' and you just can't do it. You risk alienating your DD/DIL if not the children.

Well if youre smacking someone it s not non violent is it Nankate?

LOL

It sounds as though your dd isn't being consistent if your GS is questioning her tactics in that way.

I can't imagine either of my sons or dils laying a finger on their dc's, there are so many helpful strategies available now.

Do NOT, repeat NOT go there! Apart from anything else the children are capable of playing you off against each other (maybe they are doing so already) at any rate they may be playing up even more than usual because they think they can get away with it.
Agree a plan with their mum, DDor DIL? Ask what line she wants you to take so that you can be consistent (then make sure you are)
If you feel the urge to administer the lightest tap WALK AWAY! !