Adding two motors to tricopter script

I am not sure if this is the right topic but here it goes:
I am making a tricopter drone using pixhawk and mission planner. We have realized that our motors and ESCs are not quite powerful enough to provide the thrust we need.
We tried to wire to motors into one input to make up thrust but this is causing some control issues:
Screenshot 2023-11-05 at 10.53.20 AM

How difficult would it be for me to alter the ardupilot code in order to add two more independently controlled motors?

You can and should start here: Lua Scripts — Copter documentation

Why do you keep posting the same question over and over again?!

This is my only post about coding? My previous posts were about diagnosing control issues.