Are these 8 the same variety of paniculata or different types of miculatas?

all 8 are little lime
Bill

What is your goal in pruning them? IME, unless you want to prune them for size, there's no need to prune other than to remove spent blooms. I don't have Little Lime, but my other paniculatas bloom well and don't need shaping, so I haven't seen any need to prune them.

I have never pruned my Little Lime or paniculatas either but if you are trying to get all 8 in sync heightwise, you could choose to prune them to the shortest height. Your Z7b winters will not kill the stems down to where you need to prune at 18".

However, this pruning to the same height business will become an annual chore from the sounds of it. You will need to do it 2-3 times a year probably. Something (more water, more soil nutrients, more sun, etc) is making a few of the LL shrubs grow more and you will have to keep doing the pruning regularly.