To ensure that the parathas stay soft place them in a warm casserole as soon as you remove them from the tawa/skillet and cover the casserole. If you want to add the parathas to a lunch box then remove the whole batch from the casserole while the parathas are still hot and pack them tightly in a foil. Make sure that they don't become cool while you are packing them in foil as this will make the parathas dense. In addition, using oil instead of ghee to cook parathas can help them to stay softer for longer.