You can cut all but one of the power (red) leads as is commonly recommended or you can leave them intact to parallel the outputs.You definitely need to leave all of the ground leads from the BECs intact to provide the required common ground reference for the motor control lines.
Although some engineers will disagree, generally the linear BECs used on most ESCs are entirely tolerant of being "paralleled".
Although some engineers will disagree, generally the linear BECs used on most ESCs are entirely tolerant of being "paralleled".