Cut two lengths of green wire to 3 inches exactly, and solder it into the ANT pin on each of your Feather boards.
Get out two neopixels and solder a red wire to +, a black wire to -, and a white wire to "in". Test the pixels with your Gemma tester to make sure they come on and light up in all the colors.
On ONE of the feather boards, add a small jumper wire in pins 9-10. This jumper will be referenced in the code to tell the two boards apart (transmitter vs receiver).
Once your soldering is done and all your connections are clean, it's time to upload the code to the board and refine your variables.