Clock asynchronism between base stations (BSs) and users significantly degrades scatterer localization accuracy. To address this issue, this paper proposes a multi-BS joint channel estimation and localization scheme that exploits shared scatterer information among multiple BSs. First, channel modeling in the location domain is performed by leveraging the joint sparsity of multi-BS channels. Subsequently, a multi-BS scatterer association algorithm is developed based solely on Angle of Arrival (AoA) estimates. By utilizing the shared scatterers and the geometric relationships among the scatterers, BSs, and the user equipment (UE), coarse estimates of the UE location and timing offsets are obtained. Based on these coarse estimates of scatterer locations, UE location, and timing offsets, an expectation-maximization (EM) framework is employed. Specifically, the UE location and timing offsets are iteratively refined while jointly enabling high-precision estimation of scatterer locations and channel coefficients. Simulation results demonstrate that the proposed scheme achieves significant improvements in both channel estimation and localization accuracy compared with baseline methods.