Kittens won't drink any KMR....

I have a question I hope someone can help me with. I have six kittens, I'm sure you all have seen plenty of pictures of them , and they are 2 weeks and 2 days old.
I've heard I should be trying to give them a few feedings on the side each day to help Holstein, but they are refusing the little nipple. I have a small slit in it, so I know enough is coming out. I can even see the milk in their mouth, but they hate that nipple. They cry when I try and give it to them. I know they are hungry when I try to feed them too because I wait until Holstein has been away from them for a while and when I go in there they start whining.
They appear to be very healthy, she nurses them a lot.

So is it really necessary to give them supplemental feedings? I've been giving Holstein lots of KMR each day to give her additional calories/vitamins. She drinks a can in about 3 days. I also give her kitten food and 2 packets of Sheba each day. Is that enough for her with nursing that many babies?

Should I really try and give the babies more KMR? Any advice would be appreciated.

I wanted to add that the kitten food is always available. It's just the soft that I limit. Is that okay?

If momma is nursing and they are gaining weight I wouldn't suppliment. With the food, I had dry out all the time and wet was given 6 times a day, Missy didn't really like dry food.

If you have weight them and they look healthy I see no need to supplement...