We were commissioned the redesign of a web application for real estate agencies. During the first stage of our user research, which was a contextual inquiry, we found that the form fields (or data structure) for entering a new Property has many problems. There are fields that should not be mandatory, malformed fields, fields with incorrect options, maybe missing fields, etc.
We are looking for a user-research technique or method that allows us to evaluate the existing fields and determine the necessary changes in order to adapt the forms to current market practices and customer needs. The usual methods such as card sorting would not be very useful here, as it's not a matter of labeling or sorting the fields.
Since we have seen differences of opinion between the real estate agents and some level of consensus must be achieved, I suspect we should use a quantitative technique rather than a qualitative one, but we are open to all possibilities.
(Context: This is an application for the housing market in a latin american country with thousands of real estate agents, closed to the general public, which has been running for more than a decade with little to no UI or UX updates).