use this library if you need a software Serial that could be configured in a different way rather the default 8N1 (8 bit of data, no parity, 1 stop bit).
Based from the ESPSoftwareSerial library modified to support other serial configuration options
On startup call the overloaded begin method with the following signature
void begin(long speed, int stopbits = 1, char parity = 'N', int databits=8);