Arduino capacitive touch sensor help
I think you are making a mistake initializing cs_5_7.

CapacitiveSensor   cs_4_2 = CapacitiveSensor(4,2);
CapacitiveSensor   cs_5_7 = CapacitiveSensor(4,6);


You are using same pin 4 for both Capacitive sensors. Try using different pins. I am quite sure that, this would help.