Your last diagram looks fine to me.
5V is a typical logic level voltage. The PCB holes marked 'A' is indeed where the board is powered from. The +5VDC to one of the TE (transmit enable) ports, it is sending a logic signal to the board to transmit. If JP2 on the receiver module is set to M (momentary), the relays will only be powered (i.e., they will only connect across the NO contacts) as long as the signal is being sent from the transmitter. However, if JP2 is set to L (latching), the relay will remain in the last state sent by the transmitter, even if the transmitter stops transmitting.
Hope this helps.
Edit: Don't forget to also connect either pin 2 and/or pin 4 to +5VDC in order to trigger the appropriate relay on the receiver. For instance, you could have two switches. One switch could be connected to the TE AND pin 2, and the other switch could be connected to TE AND pin 4. Then, when you pressed the first button, only the top relay on the receiver would trigger. Likewise with the second switch.