Based on the works written by O. A. Krasavchikov and V. B. Isakov, the author of the paper analyzes cases when participants of family relations engage in family acts in bad faith, thereby violating the rights of other parties, which indicates a defect in their acts. The author defines a family act as a lawful act committed by an individual possessing the necessary degree of family legal capacity, aimed at the emergence, modification, or termination of a family legal relationship. Identifying specific defects in the acts of participants in family legal relations has facilitated the distinction between fictitious and sham family acts. For example, if an individual attempts to conceal their true intentions by leveraging the legal consequences of executing a family act for personal gain, this suggests the act is fictitious. In the context of family law, a fictitious family act is understood as an act performed for appearances only. The objective of such an act is to achieve unlawful legal consequences that do not align with the essence of the legal norm, resulting in the violation of either public or private interests. The differentiation between fictitious and simulated family acts is further supported by the varying legal consequences that arise from their performance. If a family act is conducted in a fictitious manner, it should lead to its invalidity, and the resulting familial legal relationship should be deemed non-existent. In instances where the simulation of a family act is detected, adverse consequences may arise within other legal contexts related to family law. However, such findings cannot restore the original family legal relationships.