I have a mamma chicken who after the first egg hatched forgot about the rest. Do I take the chick in hopes that she will go bake to sitting or do I do nothing?
If she has already left the nest, it is unlikely that she will return if you take the chick away. Do you have or can you set up a makeshift incubator? This is a problem that frequently happens with staggered hatches.
I had this happen with me once. I left the unhatched eggs (2 of them) and mom went back to sleep on the nest with the chicks. One of the eggs hatched about 2 days after she got up to run around with the chicks. Poor chick nearly dead when I found it. You can imagine my surprise though! I thought the egg was off!
I think the best way forward now is to do as Sourland suggested and put them in an incubator and keep them warm and humid and hope for the best.
If you dont have an icubator set up a heating pad on low or put them in a box under a light but make sure you dont cook them , at this point a little low is better , they may not hatch but miricles do happen so go for it.