I worked for a company doing something similar and they used servos that were strong enough to control the plane, but no so strong that the safety pilot couldn’t overpower them if needed. I think it’s the same for any autopilot really. And there’s always a big “disconnect autopilot” button in case it goes haywire.

I think they will need to consider that situation though, if the autopilot does fail the pilot would still need to have enough skills to land the plane. Even ATP pilots have this issue where they over rely on automation too much and lose their ability to land manually in an emergency situation.