What is the ruling on praying Fajr in congregation at work, and is it permissible for one of the employees to go to the mosque while the other remains at work, considering the importance of this work?

There is no sin in missing congregational prayer in the mosque for the sake of work. It is better for one of you to go to the mosque, then pray with the one who remained at work to attain the virtue of congregational prayer, and his second prayer will be charity for which he is rewarded.