Very easy Arduino code challenge for you brainiacs to solve
You are attempting to use IO pins that are already in use by the MP3 shield.

According to your subsequent research, only digital pins 0,1,5, and 10 are available for use.

You should shy away from using pins 0 and 1 since they are also connected to the computer through the USB interface and are used for uploading sketches.  You will find that either you can't upload sketches with the relays connected to those pins, or the relays will "randomly" switch on and off while you're uploading a sketch.

Don't forget that the analog pins A0-A5 can also be used as digital pins, so you can quite happily drive your relays using any of those.