Final answer:
Isabel and Ruth are sold at the age of twelve or younger for a minimal price. This price does not benefit the parents or the kingdom due to the high cost of caring for children.
Step-by-step explanation:
Isabel and Ruth would be considered no more than twelve years old when they are sold. At this age, the merchants claim that they are not saleable commodities and would only fetch a maximum of three pounds and half a crown on the exchange. This low price does not benefit the parents or the kingdom, as the cost of nurturing and clothing them would be at least four times higher.