but I don't understand how to integrate the two, especially at the beginning of my code, where I declare the capsense pins, for example:
You can't mix those two easily. Setting the pins to some new, higher value won't work, the library is written to access Arduino pins only.
You will get away with replacing the output pin with a pin on a serial to parallel chip or a multiplexer, but you will have to modify the library to make that work. You might also get away with replacing the input pin with some type of analogue multiplexer, but check first if the timing for reading works with the desired circuit.
The way you asked those questions these adaptations are probably beyond your level of experience with programming. If you want to try it anyway, Capsense.cpp is the place to start.