HC 12 to control 5V relay
Yes and no.

To make a stable device you will need a microcontroller that will read serial data received, implement a protocol, verify checksums and so on. Your module could receive whatever from the air and if it is not veryfied at least through checksum your relay can go ON and OFF without your command.

Other methods that can be done without a smart bug (MCU :) ) will not be stable enough.

Why don't you look at the ESP12 family modules? They are WiFi compliant, can connect to your home network and have GPIO pins that can easily be connected with a NPN transistor and a couple of resistors to drive a relay.