Once the lead Financial Institution (FI) has its FATCA ID, it will not be possible for each of the member Expanded Affiliated Group (EAG) entities to log on at the same time to register. According to the retrieved information, each member FI must have its registration completed, and the lead FI will create all their member accounts and provide each member FI with its login credentials. However, only one entity (either the lead or the member FI) can access the member account at a time. This means that while the lead FI and member FIs can all be logged into their own accounts simultaneously, only one can access a specific member account at any given time.
Sources:
Instructions for Form 8957 (06/2018)
Publication 5118 (07/2021)
Notice 2013-43
