We consider a wireless network comprising multiple singleantenna repeaters that amplify and instantaneously re-transmit received signals in a full-duplex (FD) communication setting. Specifically, we study a massive multiple-input multiple output base station that simultaneously serves multiple uplink (UL) and downlink (DL) user equipment (UE) over the same frequency band. The focus is on the problem of repeater weight optimization at each active repeater to maximize the sum of the weighted minimum spectral efficiencies (SEs) for both UL and DL UEs. The resulting non-convex optimization problem is tackled using a successive convex approximation technique. To demonstrate the effectiveness of the proposed approach, we evaluate its performance against benchmark systems with and without repeater assistance. The optimized FD design achieves SE improvements of up to 4-fold and 2.5-fold compared to its half-duplex counterpart.