Hi Olushola,
It is very much possible, I’ve tried it. I successfully transmitted and received audio frequency signals. In your case, you need a circuit which decides whether to turn on or off the relays based on the presence or absence of the signal.
My ciruit was a extremely simple but little bit dangerous, since there is no actual isolation of the power lines from the circuit.
You can find lot of examples of powerline signal couplers from the net. Here is the link to one such device which I’ve found which uses optical isolation from power lines.
http://datasheet.octopart.com/0557-7700-11-Bel-Fuse-datasheet-13509475.pdf