First of all, you need to understand that job families are groups of occupations based upon work performed, skills, education, training, and credentials.
Job ladders are career progression path in your organization. You have to see particular job can move from minimum one level to maximum level. Accordingly you may assess on experience, qualification or expertise may move in dirrerent level within one job occupation shall be organised for pay bands from low to maximum.
This exercise shall be done for all job position where these positions have movement as career path or job ladder by promotions to move upwards in your organization which can be indicator as grade.
Some occupations may have limitation but due to market pricing of such jobs are specialise into ocupation like Engineers, Professionals, Finance,Commercial and Administration etc.
This is in order to maintain internal equity and external equity.
You may want to inquire and research also about employee banding and levels within banding.