Is it permissible for these men to combine the Maghrib and Isha prayers in congregation at their workplace due to rain, or is combining prayers only valid in the mosque where Friday prayer is held?

Whoever hears the call to prayer (adhan) must hasten to pray in the mosque. It is permissible to combine the Maghrib and Isha prayers when it rains, according to the majority of scholars. Scholars have differed on the permissibility of combining prayers when it rains, holding two views: The first: It is permissible to combine absolutely, whether there is hardship or not, and whether it is in the mosque or at home. This is the view of the Hanbalis. The second: It is not permissible to combine except when there is hardship and harm. This is the view of the Shafi'is. Based on this difference, according to the Hanbali view, your prayer is valid, while according to the Shafi'i view, it is not permissible for someone in your situation to combine. And whoever combined before this, there is no blame on him and he is not commanded to repeat his prayer.