This study investigates the hydrogen-assisted crack propagation mechanisms in FeNiCr medium-entropy alloys (MEAs) through molecular dynamics (MD) simulations, focusing on the roles of hydrogen concentration, chemical short-range ordering (CSRO), crystallographic orientation, and loading rate. By extending the Rice-Thomson framework, it is demonstrated that hydrogen increases the energy barrier for dislocation emission, suppressing crack-tip plasticity. Compared to random solid solutions, CSRO-structured FeNiCr alloys exhibit a higher critical stress intensity factor for dislocation nucleation and promote hydrogen segregation near the crack tip to form a hydrogen atmosphere. At lower hydrogen concentrations, hydrogen facilitates dislocation glide, consistent with the hydrogen-enhanced localized plasticity (HELP) mechanism. At elevated concentrations, however, the hydrogen atmosphere strongly pins dislocations, leading to highly tortuous dislocation lines.