The efficient management of network resources together with the Quality of Service (QoS) control of real-time multimedia group communication sessions in Next Generation Networks (NGN) is still a challenging research goal. The unified control of the session quality level, distribution tree allocation and network resources in NGN will increase the user satisfaction, reduce operational costs, optimize network resources and maximize the profits of providers. This paper introduces the Multi-user Aggregated Resource Allocation mechanism (MARA), which supports a dynamic control of surplus class-based bandwidth and multicast resources in a scalable way, while assuring the minimal quality level of multimedia group communication sessions. In comparison with existing works, MARA significantly reduces signalling, state and processing overhead. In addition, simulation results present the benefits of MARA by improving the network performance under re-routing conditions.