This communication addresses multicriteria sorting decisions to be made by a group of decision makers, without assuming that complete and precise information exists about parameters related to their preferences, such as criteria weights. In many decision-aiding processes, the facilitator does not have the possibility to use multicriteria aggregation models with complete and precise information about preferential parameters such as weights, thresholds, etc. This difficulty is amplified in contexts with multiple decision makers because of the possible disagreement between them. We propose a methodology to help the group reach a common sorting model, in a context where numerical information raises disagreement and is hard to obtain. It is based on an aggregation / disaggregation approach for the ELECTRE TRI method, implemented on the Decision Support System (DSS) IRIS. Aided by IRIS, the group may iteratively reach an agreement on how to sort some exemplary actions, preserving the consistency of these sorting examples both at the individual level and at the collective level.