Two 3w 5d old kittens widely different in size, whats average weight?

My cat had three kittens at two weeks old we had a kitten die. it was the runt and was expected, then immediately following that (or maybe before that, I hadn't been weighing them then) the largest kitten stopped growing and the other seemed to explode weight-wise I started supplimental fluids then supplimental feeds. I now feed her 4-5 times a day and everytime I do she is just panics trying to get to the eyedropper. She weighs 5.2 oz now and her sister (the big one) weighs 12.8oz. I do not suppliment the bigger sister at all and I have seen both kittens nursing from momma cat. What are average weights for kittens 3,4,5,6 weeks? Momma cat is still caring for both babies as far as cleaning and stimulating bowels. this just blows my mind how one kitten can thrive and the other can not.. and info is greatly appreciated!!