Qi charging multiple devices with single transmitter
The Qi technology doesn't allow for multiple devices on a single transmitter.

There is considerable handshaking between a transmitter and receiver. The receiving device transmits control information to the transmitting device, which then adjust its own power transmission parameters. This repeats, if I remember correctly, every 250 ms. In this way, the power transfer can be optimized with single-direction communications.

There is nothing in the Qi spec that allows for multiple devices or device addressing, and so multiple receiving devices would simply try to talk over one other's transmissions and break the control loop.

The communication method is pretty clever! The receiver varies the impedance of its own coil by switching in capacitors onto the resonant circuit. These perturbations are seen by the transmitter as differences in current through the transmitting coil. Here is an example from TI's BQ51003 datasheet: