What is the ruling on congregational prayer with those who establish the prayer before its appointed time, and is it obligatory for us to pray with them, or should we wait for the time appointed for us?

You are not obliged to pray with the first passing congregation, nor is it forbidden for them to establish their congregation before yours, for two reasons: First, repeating the congregation is not disliked in mosques that do not have a regular imam, and the same applies to workplaces' prayer areas. Second, prayer areas in workplaces and government offices do not have the rulings of a mosque. A prayer area is not a mosque; i'tikaf (spiritual retreat) is not valid therein, a person in a state of janabah (major ritual impurity) is not forbidden from staying there, nor does it have a "tahiyyat al-masjid" (mosque greeting prayer). Therefore, you are not obliged to pray with the first passing group, and you may wait for your colleagues.