Single Serial to multiple Serial transfer using 8051

[Anupam]

I have been assigned a project to make a system wherein there are three
8051 microcontrollers and their serial interfaces connected to
different devices. However, when one device starts transmitting, the
8051 connected to it will become the master and will transfer the same
to the other two microcontrollers using some common bus. There should
be some kind of arbitration so that only one microcontroller can
transmit at a time. Can someone please give me some idea as to where I
should start with? I am totally new in this field.....I have taken the
embedded systems course in my college as I am interested in this field.

Thanks in advance!