What kind of formula?

So Ive decided that the kits need some formula along with the regular food to fatten them up. Skye is nuring them once a day at the most at this point and only 2 at a time so only 2 kittens get milk a day. Though they are healthy and active Im worried that they just arent getting enough since they are so small. So yesterday I went to Petco to clean out cat cages for the rescue I work with and was going to pick up some formula. But Im confused on what kind would be best for them. I was going to get KMR but then someone there said no Just Born is better. But I thought that was just for very young kittens. My rescue doesnt think they need the milk so they arent gonna give me any. So I gotta get it on my own. Which kind would be best for 7 week old kittens?

the just born is normally ok for them up untill there 8 weeks old i belive. but kmr will be just as good.

I'd go with the KMR.