This paper introduces an innovative framework to address the dual-blind deconvolution challenge within joint radar-communication (JRC) systems, leveraging the Alternating Direction Method of Multipliers (ADMM) to estimate unknown radar channels G (or communication channel H) and transmitted signals X under convex constraints. The approach iteratively refines G (or H) and X estimates alongside auxiliary and dual variables, employing proximal operators to manage potential non-smoothness in the constraint functions. This method stands out for its computational efficiency and adaptability to a wide array of signal processing and communication problems where blind deconvolution is pivotal. Performance analysis reveals a notable reduction in communication mismatch and demonstrates significant improvements in key system metrics such as the Signal-to-Interference-plus-Noise Ratio (SINR), spectrum efficiency, and radar mutual information, particularly within the context of 5G millimeter-wave (mmWave) systems. These results underscore the proposed framework's potential to enhance the synergy between radar and communication functions, promoting more effective spectrum utilisation and environmental sensing capabilities in next-generation wireless technologies.