Is is possible to communicate over 1 XBee to multiple microcontrollers?
If hardwired connection between controllers MC2 ... MCn is acceptable (as appears to be what you are saying) then there are numerous hardware solutions available which would work on even very bottom end uC's (microcontrollers).

Interconnecion could be by SPI, Asynchronous serial (TTL level "RS232), IIC (less likely) and more. RS422 family transmitters/receivers/transceivers allow multidrop serial with good range and noise immunity.

MC2 could be identical to MC3...MCn or could be more capable if required to handle the communications task.

Communications could daisy chain from MC2 - MC3 - MC 3 ... or could star radiate from MC2 or, if there are many uC's could have a multi level star.

Issues to consider in choosing best scheme are data rate (uC's x data bits per display x updates/second), physical distances between uC's, RF link range wanted, powering and more.

If total data rate was modest you could use a single data stream with all stations on it and each accepts only it's own addressed "packets". As number of displays or and or bits per display rise you may wish to partition the data stream at MC2 so that MC3 ... see only a subset of total data or only their own data.

Useful to know:

Data bits per display.
 Max number of displays.
 Refresh rate per second.
 Powering.
 Physical environment
 Distances between stations.
 ...