The red-tails are still building their nest. You will sometimes see them at the nest adding new sticks and materials as well as cleaning out debrise from last year. Also look for them perching on the railing above the nest. Often they are out of view of the camera. Last year they laid their first egg on March 6th, but the timing can vary considerably based on the weather and other factors.
Red-tails typically lay from 1-4 eggs. Eggs are laid approximately 24-48 hours apart meaning that in a large clutch there can be as much as six days age difference between the youngest and oldest nestlings.
However, red-tails sometimes do not begin incubation until they lay their entire clutch. The eggs will not begin developing until the parents begin incubation. There is no need to be concerned if you see an egg in the nest early on that is not being incubated---it just means that they are waiting until more eggs are laid.
Once incubation begins however, the parents will need to attend to them until they hatch. If wait until all the eggs are in the nest to begin incubating, the young will all appear to be the same age, but they begin incubating each egg as it is laid, age differences will be more apparent.
Incubation lasts 28-32 days. The female does the majority of the incubating with the male providing food. After hatching the young spend on average 44-46 days in the nest before attempting their first flights.