The negatively charged boron vacancy ($V_B^{-}$) in hexagonal boron nitride (hBN) is a promising spin defect for quantum sensing in two-dimensional material systems. Previous hBN experiments have mainly exploited the two spin-triplet ground-state single-quantum transitions separately. Here we implement a double-quantum driving scheme based on simultaneous resonant microwave excitation of both ground-state single-quantum transitions, establishing coherent control of the $\Delta m_s=2$ manifold in a $V_B^{-}$ ensemble. We compare the resulting double-quantum response with the corresponding single-quantum protocol under identical experimental conditions. The double-quantum protocol enhances the optical readout contrast and yields a 2.6-fold signal-to-noise improvement in AC magnetometry. We further use the double-quantum relaxation channel as a differential probe of electric-field and strain noise, showing that the present data are compatible with correlated-surface or volume-distributed fluctuations, while short-range uncorrelated surface-noise models are disfavored within the assumptions of our analysis. These results establish double-quantum coherent control and frequency-resolved AC magnetometry in hBN spin ensembles, and identify the sample-dependent measurements needed to determine the microscopic origin of the dominant relaxation channels.