That area is absolutely suitable for 4 hens, but I would personally worry that without actual free ranging, the Cornish will not be able to keep from growing. The food resources available in that space will be quickly consumed so you will need to provide food.
Perhaps someone with more specific feed experience will chime in for your layers, but you will have to be on a very very regimented feeding program and will have to figure out how your Cornish doesn’t consume the rations for the other birds.
One additional question, are you sure the Cornish is a hen?