[Wombii]

Someone should double check this answer to make sure I'm not missing anything.

Your method should work, but make sure you only have 1 ESC red wire connected to the receiver (or together) so the BECs aren't interfering with each other.

Background theory:
ESC sucks power from the battery through the thick batter wires and supplies the motor and internal BEC. The BEC lowers the voltage to 5-6 volts and supplies the receiver with power through the red wire in the servo connector. The receiver supplies the servo signal back to the ESC through the white wire, and the return path for both red and white is through the black ground wire in the servo connector. We don't know how well the BEC plays when its output is connected to another power source, so to be safe, we don't want to connect it to another BEC.

Servo wires:
Cut or unplug the red wire in the servo connector from 3 of the 4 ESCs. Then use Y-harnesses as planned. You may lose some power from the BEC through all those connections, so consider soldering a custom harness.

Battery wires:
Connect the red wires together. Connect the black wires together. The ESCs should be connected to the battery in parallel.