I started leaving a few eggs in the nest box's and marking them (so I knew which were laid when I gathered eggs for the day, and which to leave in the nest box)
You could use golfballs as fake eggs instead, then there's no risk of confusion, they won't go off and explode over time, and they will work just as well as a clutch of real eggs to stimulate broodiness.
They've been in there for about a week now, and no one is showing interest in sitting on them
Be patient.
Is there a way to entise one of them to go broody and start sitting?
What you are already doing is the traditional method: leaving a clutch of eggs in a nice clean, dry nest. Locking a preferred hen in on them, also traditional practice, apparently works, but isn't my style. I wait till they choose to go broody.
Am I doing this too early in the year. Should I wait until it's a little warmer weather (Live in Maryland)?
I don't know what the Maryland climate and weather is like, but here my broodies rarely start before late spring, late April/early May, with hatches through the summer, i.e. June, July, August, sometimes September. They instinctively know what's the best time for chicks foraging (mine are out and take the chicks onto grass the day after hatch), with lots of natural insect food around and nice warm weather for chicks.
All my birds are heritage/rare breeds, and there's no breed pattern among them for who goes broody, who doesn't. I don't have Silkies, who have a reputation for broodiness, but also, not often mentioned, lay very few and quite small eggs, so suitable if you want a broody machine but not much use as a layer. Of the breeds you've got, I had an RIR and have an Araucana (which is one of the foundation breeds of the Amerucana), and both have gone broody, and been excellent broodies. Personally I'd avoid using any hen with feathered feet (in general, but especially as a broody).
Good luck! Having a broody raise chicks is the best bit of chicken keeping in my experience.
