The possibility of frequency stabilization of two gyrotrons with similar parameters when part of their radiation is reflected from an external high-Q cavity is shown analytically, and the stability of stabilized states is investigated. Analysis of stationary states in which the generators radiate coherently shows that the radiation frequency can be stabilized if the quality factor of the external resonator is high enough. In this case, changing the parameters of the system leads to significantly smaller changes in the generation frequency than in the absence of reflections: in a fairly wide range of parameters, the gyrotron radiation frequency can be kept within the band of the external resonator. As the eigen frequencies of gyrotron resonators increase and decrease, hysteresis and jumps in the radiation frequency can be observed. A study of stability at the optimal delay phase shows that frequency-stabilized states are stable. When the deviation from these states is small, the disturbances in the amplitudes of the gyrotrons decrease most quickly. At the next stage, over a longer period of time, stationary values of the gyrotron phases are settled. At the last, longest stage, stationary values of the amplitude and phase of the external resonator are formed.