With the rapid growth of the wireless network and the function of mobile terminal, the services which need the wide bandwidth like video streaming are expected to be used extensively over wireless networks. Overlay multicast in which a terminal relays the content to other terminals is able to deliver it to enormous terminals. However, due to instantaneous disconnection and rapid bandwidth decrease in wireless channels, we need a different architecture from the ones used for fixed environments. In this paper, we propose a new overlay-topology design, where we use the instability information of mobile terminals such as the disconnection rate and the changing range of physical transmission rate determined by the physical conditions including radio signal strength and handover. Moreover, to reduce the performance degradation caused by instantaneous disconnection and rapid bandwidth decrease and to obtain the route-diversity gain, the proposed method assigns more logical links to the terminals that likely suffer from the impact, which results in the improvement of the received stream qualities of the terminals. This paper also shows its superiority to the conventional methods in terms of service quality and robustness from the simulation results using a wireless channel-quality model we newly propose.