The fatso on the bottom is the most voracious eater (and pooper). The one above it is about 25% smaller.
I give them fresh milkweed leaves every day - the tenderest ones from the top of the plant. I often throw in another leaf to make sure they have enough to eat through the night.
They reside in this container that Scooter was given many years ago. When we have more than 3 or 4 larvae, I also use a large mayonnaise jar. When the larvae are smaller in girth than the holes in the top, I use a piece of pantihose across the top anchored by an elastic band.