I'm getting even more lazy.

Dealing with signal levels of the servos when they are turned of gets annoying so... What about driving the motors directly ?

The servos can be unscrewed and we can access the two wires, which are easy to desolder. So all I need is a dozen of motor drivers ("H bridges") that can hold a few hundreds of mA. But... only one motor needs to be driven at the same time.

I have enough Allegro A3968ELB (dual H Bridges) for this purpose but that still sounds overkill.

Another idea is to share the sensors' selection with the motor drivers' outputs. It's a bit tricky...

I am very tempted to implement those functions with relays. They draw a lot of current but convenience of design and simplicity beat many other constraints, and I don't want to have to program anything...