As I already read, driving two motors by the same output -which is usually perfect for stepper motors- on ODrive isn’t such an good idea.
However, If two motors on a single shaft are connected at the two output ports, it is possible to drive them both from the same encoder? Can this configured easily by software?
Or is it allowed, eg. for AMT 102 encoders, to connect the encoder outputs to both of the ODrive encoder inputs?
Yup.
No.
Yes. Calibrate one axis, then put it in idle, then calibrate the other axis. Now they should both track 
Thanks!
I’ve now also managed to drive two motors from the same output it seems. After mounting the motors to a common axis I probed all windings of both motors by scope while turning manually. I then joined the cables of both motors in the most matching fashion, and connected them to ODrive this way.
After calibration it seems to work quite well. Idle current is low and control is fine. I don’t know if both motors are delivering equal power, but they seem to heat up equally if stressed.