Group multi-criteria decision-making in environment-related problems is faced with important aspects such as competencies of the members of the group, demonstrated consistencies while making judgments, compatibilities with derived group decisions, etc. In this paper, we present an approach and methodology for evaluating the quality of group members based on their consistencies and deviations from the group decision. While individually making decisions, members of the group demonstrate how consistent they are. Once their decision is aggregated into a group decision, it is possible to assess individual deviations of decisions from the group decision. The members of the group can be treated as alternatives in the multi-criteria environment where criteria for assessing their 'quality' are performance indicators such as Euclidean distance, minimum violation, conformity, and Spearman's rank coefficient. Preference schemes applied to sets of performance indicators offer manipulations that may eventually lead to justified exclusion of odd (e.g. consistency - inferior) members and further changes in deriving the group decisions. An example is presented in which importance for society is assessed for six endangered Ramsar sites in the northern part of Serbia. Ramsar sites are considered as environmental systems and assessed by seven experts using AHP. Based on their consistency and deviation parameters as criteria, evaluation of the quality of members in the group is performed by the TOPSIS multi-criteria method. The discussion part of this article is devoted to the possible use of the DEMATEL method and entropy concept in supporting the group decision-making processes.