One stepper motor of two getting really hot
The L293D is only a driver that switches the supplied voltage to the load (motor). It has no current control, like chopper,... So basically when the motor is at standstill the current is limited only by its winding resistance. If it is spinning then the current is lower, since the back EMF voltage builds up:
$$V_{supp} = I\cdot R+V_{BEMF} $$
$$I=\dfrac{V_{supp}-V_{BEMF}}{R}$$
$$V_{BEMF}=k_e\cdot N_{RPM}$$  

therefore at N=0:

$$I=\dfrac{V_{supp}}{R}$$