Wireless edge caching and rate splitting multiple access (RSMA) are widely acknowledged as effective techniques for reducing backhaul latency and transmission latency, respectively. In this paper, we consider the cooperative networks involving multiple BSs. Specifically, when a base station (BS) receives a user request, if the requested file is not found in the local cache, the BS can first request the file from other BSs. If it still cannot be obtained, then it requests the file from the back-end server. This approach can further reduce the pressure on the backhaul link and decrease latency. Based on the cooperative caching among BSs, we focus on the average latency minimization in RMSA-aware multi-BS cooperative networks, considering joint cooperative cache placement and RSMA resource management. The formulated problem is a non-convex mixed-integer non-linear programming (MINLP) problem. To address this, we decompose it into two subproblems: the optimization problem of caching policies and the optimization problem of allocating RSMA resources. The optimization problem of cache strategy is reformulated as multiple 0-1 knapsack problems, and we propose an iterative algorithm based on dynamic programming approach to solve this problem. Furthermore, we introduce an alternating optimization approach incorporating one-dimensional exploration to tackle the RSMA rate and power allocation problem. Extensive simulation results substantiate the superiority of our proposed scheme compared to various baseline approaches.