Hi Granny,
I am pretty new around myself. My hat is off to you for taking on such a tough task. How old are the Grandchilden? I mean that kinda makes a difference as to what advise you get, I think.
The younger they are would be better, because not so set in their ways (usually bad ways at that). Anyway, if I could give you any advise is (which you probably know this) if you don't mean it, don't say it. If you do mean it, follow through and do it.
It's like this, have you ever watched Mom's or Dad's in stores with the little kiddos? The kid is fussing or doing something they know darn well they aren't suppose to do but hey, lets test the adult. Anyway.....the adult says don't do that....and then just turns away as if they hadn't said anything and the adult really doesn't wanna see if the kiddo is listening or not. It's like, I did my duty I told them not to do it. Well, guess what, the duty part of the parent is inforcing what you say. Watch them to see if they listen and if they don't well, then consequences. That way the children know when you say something, you really do mean it. If you follow that rule, you won't spend the rest of your life yelling at children who aren't listening anyway because what you say you don't follow through with and they hear so much yelling they have turned your voice off in their head.
I have two children 20 & 18 year olds. I followed that rule from day one. For me it worked. Of course, each child is an individual so modification may be in order, but if you say it, mean it. I used the counting a bit to give them a few seconds to comprehend what I said and I also used Time Out in a Corner - the rule for that is never any longer in the corner then their age. After that the attention span has gone for why they were even their. When time to come out of corner I always discussed why they were in their and how to improve for next time.
Anyway, that's my book
Hope it helps you a bit.
I know, you're thinking wow, how could she know anything about raising children since mine are not children any longer. Well, technically I still have a small child. The 18 year old is handicapped. He has the mind and temperment of a 3 to 4 year old, so see, I've had plenty of practice and have worked very hard with him. He is very well behaved, I am proud to say, and now he is so use to knowing that when Mom says no she means no that all I have to say is "You aren't listening to Mom?" and he say's "I'm listening" and gets back on track. I tell him, "Thank you, you're a good boy" (he likes to hear that) - Praise is good as well. (Never say they are bad, if you hear it enough, you believe it and act it)
Well, good luck and hope I helped.
That is the best advise I can give you.