Is the ruler entitled to order his companions to pray in congregation as an obligation, or is there no obedience to a creature in disobedience to the Creator, especially after one of them has prayed alone a short while before the proposed congregational prayer?

The leader of a journey must be obeyed in matters pertaining to the journey. However, it is permissible to disobey the leader of a journey and offer the prayer, because the Sunnah indicates the permissibility of performing the prayer at the beginning of its time if the leader delays it. And if it is permissible to disobey the greatest Imam in delaying the prayer, then disobeying the leader of a journey is even more permissible. This disobedience is further emphasized if he delays the prayer until the time of اصفرار (when the sun turns yellow, indicating the approach of sunset).