You didn't mention how the age of your kittens but you really should not force their eyes open.
If they had an eye problem...like crust or eye infection, I would use a damp warm washcloth or cotton balls...make sure washcloth is soft and gently wipe...don't rub.
Is the mother cleaning them? She should be licking their little faces including their eyes which will help them open up.
I know how you want to help them but it is much better to let nature take its course. You could do terrible damage if you don't know what you are doing. If it looks like any of them have infected eyes with pus or stickiness then take them to the vet. Eyes are far too precious to mess about with.
What kind of cat do you have? My Siamese queen just had kittens nine days ago. One of my kittens opened their eyes at two days old. At nine days they all have their eyes completely open. I think that eye opening depends of many factors. Dark reared kittens open their eyes before light reared kittens. I believe that I have read that siamese open their eyes earlier than other breeds.
Meghan