How old are those two "hens"? Are they laying yet? Age (maturity) has an effect on when and where they sleep.
Chicks sleep on the floor in a brooder. My broody hens keep their chicks on the coop floor at night until they take them to the roosts. Are you sure "How should I get them to roost so they won't sleep on their poop" is all that valid a concern? That it really is a problem? Many people on this forum think it is. I personally don't worry about it. In my opinion they will roost when they are ready. As long as they are not sleeping in the nests and are some place safe from predators I don't care where they sleep.
If you want to try to train them to roost, after the coop is too dark for them to be able to see, put them on the roost. As long as it is dark they should stay up there, just use as little light as you can while you do that. If they are ready to roost and are OK where you are putting them they should start going up on their own fairly soon. Just be consistent.