The Republic of Korea became the first country in the world to have next-generation long term evolution (LTE) public safety networks, and South Korea’s evolution in critical communications has taken the lead as well. However, the same 700 MHz frequency band is allocated to the LTE-based public safety (PS-LTE) network, the LTE-based high-speed railway (LTE-R) network, and the LTE-maritime (LTE-M) network, and hence, extensive interest and practical research into co-channel interference management schemes are immediately required. This paper focuses on multi-layer next-generation public safety networks and employs efficient mission-critical user priority-based resource allocation schemes to resolve major challenges, such as co-channel interference, mission-critical user requirements, quality of service (QoS) prioritization, etc. We utilize coordinated scheduling (CS), coordinated multipoint (CoMP), and intercell interference cancellation (ICIC) under the radio access network (RAN)-sharing environment to analyze the overlapping next-generation PS-LTE, LTE-R, and LTE-M networks. CS CoMP is implemented between the three LTE public safety networks to boost cell-edge-user performance by muting the neighboring interfering base stations. This accomplishes a tremendous enhancement in system throughput for coexisting next-generation public safety networks. By employing ICIC with CS CoMP under the RAN-sharing environment, the best interference and outage performance can be attained for coexisting PS-LTE, LTE-R, and LTE-M networks.