role of a grandparent

Hi Nicholeen –
I'm sorry to submit this question again last-minute; I live abroad and I know I am sending this to you in the early hours of your morning!
I have four grown children. My "baby" is almost 19! Two of my children are married and I have three very young grandchildren. Both my daughter and DIL are very interested in your approach and ask for ideas and feedback from me as they encounter parenting challenges; that is why I decided to take your TSG online course – so that I could become a better grandparent and also have some options to offer my daughter and DIL when they ask me.
I'd appreciate it if you'd talk a bit about the role of a grandparent. I want to be there for my children and grandchildren, but I don't want to dominate or take over in any way, because the parents are in charge, and sometimes this balance can be tricky.