Problems with running multiple ESC
You have two copies of your program sharing one physical resource, the serial port input to the Arduino.  It is by chance which of the two copies will receive and process the input data.  So this approach will not work dependably.

Semiphoras are often used when sharing hardware among several programs.  However you are not only sharing hardware, but also the data being sent to the Arduino.  And the data will only be sent once.

In this case, you need to handle the data once in code that is separate from the 2 instantiations of the ESP class.  That is, you need to process the received data once and pass that processed data to the appropriate instantiation of the ESP class.