Seems to be plenty of milk...
The surviving pair are nursing very well, mama's eating a lot of food, and she seems to have a good milk supply. Oh well...everyone say a prayer that the last two hang in there. They are very large and plump.
PRAYERS FOR THE LITTLE ONES!
I remember when I was a kid and one of our cats had babies (before Mum was educated on the positives of desexing!) and they all got sick ... I held one of the little precious ones until it passed away, and it took me ages to get over it. Fortunately, the rest of the litter and Momma cat survived what turned out to be a flu type bug.
We didn't know what it was until we got them to the vets, plus the vet said the rest of the kittens would have died had we not gone to the vet and got them on meds. Have you taken Momma and babies to the vets or is this logistically impossible?