It doesn't matter how far apart the eggs were laid. They don't start to develop until incubation has started. That's how a hen can take 10 or more days to lay her clutch before she starts setting. If they were put under the hen two three days after the first ones, that will give you a "staggered hatch". That's a little easier to manage with an artificial incubator, but not a good plan with a broody. She is programmed to set anywhere from 1-3 days after the first chick hatches, then take those that have hatched off the nest to teach them to eat, drink, and do other chickeny things. She figures any that haven't hatched at that time won't.
Have you candled the 4 remaining eggs? Is there any sign of life? If those eggs were set at the same time as the others, I'd guess they have died in the shell. It happens sometimes. If you don't hear any peeping or see any signs of life when you candle, I'd dispose of them soon. If you have a staggered hatch going, I'd wait until maybe 2 days or so past their expected hatch date, then dispose of them if nothing happens.