The emergence of Network Function Virtualization (NFV) greatly improves the convenience of network layout, and at the same time reduces the service cost for operators. Currently, many studies on NFV layout focus on one-to-one unicast communication and cannot be extended to multicast. Therefore, in this paper, we are committed to exploring the joint problem of Virtual Network Function (VNF) layout and path selection in multi-source multicast. In addition, we take into account bandwidth and latency constraints, for they are the vital indices of Quality of Service (QoS). To solve this problem, we design a heuristic algorithm, named Multi-Source Multicast Tree Construction (MMTC). The algorithm aims to find a common link to place the Service Function Chain (SFC), a chain composed by multiple VNFs in rotation manner, so that the deployed SFC can be shared by all users, thereby improving the resource utilization. We then evaluate the performance of the proposed algorithm with different methods in four real topologies. Simulation results indicate that, compared to other heuristic algorithms, our design effectively reduce the total cost of services.