Y3 VTOL Forward motors access

Hello, I made a VTOL plane with three tilting motors! This plane can switch from vertical to horizontal flight by tilting the motors forward. The front two motors have folding propellers that can turn off and let the back motor take over for maximum efficiency. However, I need some help with controlling the motors. I want to be able to turn off the front two motors, motors 1 and 2, when I am in FBWA or manual mode. Is this possible? How can I do it?

I appreciate your time and help very much.