The HC-03/05 are Bluetooth modules were designed for serial communication. Note that these implement the classic version of the Bluetooth stack, not the Low Energy 4.0+ version of the standard,
By using two complementary modules, one master and one slave, you will be able to pair them and connect two independent serial streams (full duplex), one stream in the direction master to slave and the other stream in the direction slave to master.
An alternative to the previous is connecting another device (for instance, a mobile or a PC bluetooth dongle) to one of these modules which will act as master/slave.
The AT command set available for these modules, as far as the documentation goes, does not allow multiplexing: sending multiple streams (more than one), simultaneously, in a certain direction (for instance, master to slave).
A possible solution is to do the multiplexing yourself in either end of the communication, not in the bluetooth module, but outside of it,
- Let's say you connect a mobile application (running Android or iOS) with one of these modules. You could easily create your own message format for the serial communication, prepending an integer number which will indicate the number of channel.
A simplistic and very compact message format suitable for serial communications is the TLV (Type-Length-Value), which you may use for such an application,