Hi @mikromidas. That is a nice holder for the motor driver. I see that you are using the original v7.0.0-beta1 electronics drawer. We had some issues with that and the Sangaboard motor driver, so this will be changed in the next release. The new version gives a bit more space, but also moves the position of the mounting points for the drawer in the microscope stand and adds a convenient mounting point for the nano version of the motor driver. This is discussed in Sangaboard v0.5 now available - post 50.
The motors should not run that hot, and if they are then this is one of the failure modes that can draw too much current from the Pi. As you are using a Nano that will be powered by the USB-data connection to the Pi, be aware that this means that the Nano 5V pin is power from the Pi, so all of this excess heat from the three motors is coming from drawing excess current through the Pi board.
In previous discussions of hot motors (see the link in post 5 of this thread) it seems to be about particular batches that draw too much current, so not to do with the software. I have never had hold of a bad batch of motors, so I don’t know the characteristics. However the motors should never be more than slightly warm even when always using a holding current. The simplest solution is probably to send the motors back as faulty and get some other ones.