Of the two new kittens, one was dead when I found them but the other one is doing very well and is almost the same size as the kitten born 9 days before.
The mother cat is very young, probably only 7 months old so I did not know if she would know what to do but the mothering instinct has kicked...
It just happened to my cat, Miss Chiff. 3 kittens arrived 9 days ago and two more last night, the two new ones are about the same size as the survivor of the first litter. I was dumbfounded to find two more kittens so late in the process.