Recently, halide double perovskites (HDPs), such as Cs2AgBiBr6, have been reported as promising nontoxic alternatives to lead halide perovskites. However, it remains unclear whether the charge-transport properties of these materials are as favorable as for lead-based perovskites. In this work, we study the mobilities of charges in Cs2AgBiBr6 and in mixed antimony-bismuth Cs2AgBi1-xSbxBr6, in which the band gap is tunable from 2.0 to 1.6 eV. Using temperature-dependent time-resolved microwave conductivity techniques, we find that the mobility is proportional to T-p (with p ≈ 1.5). Importantly, this indicates that phonon scattering is the dominant scattering mechanism determining the charge carrier mobility in these HDPs similar to the state-of-the-art lead-based perovskites. Finally, we show that wet chemical processing of Cs2AgBi1-xSbxBr6 powders is a successful route to prepare thin films of these materials, which paves the way toward photovoltaic devices based on nontoxic HDPs with tunable band gaps.