The optimization and management of delay damages in project clusters, particularly under the constraints of Non-contractual Risk Participation Equilibrium (NCRPE), represent a significant concern for project owners. The issue is especially pertinent given the nonlinear relationship that exists between contract project delays and the collective overdue damage costs incurred by multiple stakeholders. Firstly, the study initially delves into the theoretical and practical dimensions of the deficiencies inherent in calculating collective overdue damage costs within multifaceted stakeholder environments. Subsequently, it explores the intricate nonlinear characteristics of these costs under the constraints imposed by NCRPE. An equilibrium optimization model is then developed for the initial phase of NCRPE prior to the implementation of project clusters. A discrete Markov process has been utilized to characterize the states of contract projects within the cluster and compute the nonlinear probabilities associated with collective overdue damage costs. The objective of this study is to minimize costs arising from contractual uncertainties by formulating a sophisticated second-phase nonlinear optimization model that addresses collective overdue damage expenditures throughout the project execution phase. This endeavor will also delineate solution methodologies that are adaptable across diverse scenarios. The research findings indicate that nonlinear optimization yields superior outcomes in comparison to linear methodologies, particularly with regard to the cumulative costs associated with overdue damages. The proposed model effectively mitigates the delay damages incurred by owners due to contractual uncertainties under current regulations. These results provide a foundation for optimizing collective overdue damage expenses within multi-stakeholder contexts and formulating corresponding management guidelines pertaining to such expenses.