The in-band wireless backhaul that shares spectrum resources between fronthaul and backhaul is a promising method for unmanned aerial vehicle-mounted base stations (UBSs) to provide wireless services with limited resources. However, the existing works mainly considered the out-band wireless backhaul, where the resources of fronthaul and backhaul are allocated separately. Moreover, the UBS placement methods usually focused on the optimization of fronthaul while neglecting the backhaul. In this letter, a placement algorithm that jointly optimizes the resource allocation and user association for multiple UBSs with in-band wireless backhaul is proposed. In particular, the joint optimal resource allocation for both fronthaul and backhaul is derived using convex optimization theory. Given the optimal resource allocation, an equivalent spectrum efficiency is defined to simplify the optimization problem. As a result, an effective algorithm is proposed by solving the user association problem and UBS placement problem iteratively. In addition, simulation results are provided to verify the efficiency and effectiveness of our proposed method.