This paper presents a novel optimal sensing parameter design protocol for ultrasensitive, ultraweak magnetic field detection in quantum magnetic sensing. Conventional adaptive algorithms or formula-based search methods have limitations in efficiency or convergence to optimality when the signal of interest (SoI) range is wide and the quantum sensor is subject to physical constraints. To address these limitations, we propose a novel protocol that utilizes a two-stage optimization method. In the first stage, a Bayesian neural network with fixed sensing parameters is used to narrow the SoI range. In the second stage, a federated reinforcement learning agent is designed to fine-tune the sensing parameters within the reduced search space. Our evaluation under the challenging task of single-shot reading of NV-center electron spins within a limited total sensing time yields wide-range DC magnetic field estimation with significantly improved accuracy and resource efficiency compared to existing techniques.