To get the Staircase construction started, Gustav Iron had to assign around 20 unemployed men as an aid on other tasks, in order to spare some professionals for this one. A 10 meter tall Staircase would be too risky to be trusted primarily on the Experienceless. People will walk up and down these Stairs for months to years depending on how big this cave actually is, it could be predicted more accurately after searching down deeper sections.
So instead he trusted the responsibility on 5 Construction Workers that came from Pameres Kingdom, they are quite experienced and can for sure be reliable for such a potentially dangerous task. Apart from the 5, he also put 2 of the newly hired apprentices. Best described, experienceless (On this Craft.) men from BaleTown. But compared to the 20 Farmers who have no experience at all in Construction, they can prove a bit more useful. The Farmers are doing these tasks just temporarily after all.