You can only control two servos independently with the Pi's hardware PWM.
GPIO 12/18 share a channel.
GPIO 13/19 share a channel.
The same settings apply to GPIO which share a channel.
E.g. If servo1 is on GPIO12 and servo2 on GPIO18 they will get the same signal (same frequency, same pulsewidth).
pigpio supports the hardware PWM features of the Pi. So you ...