Multiple slaves with identical address on multi-master I2C bus
The I²C specification say about the general call address:


  The general call address is for addressing every device connected to the I2C-bus at the same time. However, if a device does not need any of the data supplied within the general call structure, it can ignore this address by not issuing an acknowledgment. If a device does require data from a general call address, it will acknowledge this address and behave as a slave-receiver. The master does not actually know how many devices acknowledged if one or more devices respond. The second and following bytes will be acknowledged by every slave-receiver capable of handling this data. A slave who cannot process one of these bytes must ignore it by not-acknowledging. Again, if one or more slaves acknowledge, the not-acknowledge will not be seen by the master.


At the lowest level, the I²C protocol does not differentiate between slave addresses; all the read/write/ack stuff behaves the same.
So your slaves will work for the group address like for the general call address.