My 2 cents:
1. Two motors for one shaft is not recommended because one motor will have more load (no motor can be exactly the same, even if same type and size) including induction motors.
2. Induction motor speed depends on electrical power frequency (and number of motor poles). But you can install bigger motor pulley & smaller shaft pulley - but this will make your torque lower.
3. More torque is certainly, since you use 2 motors. You can get higher torque by using smaller motor pulley & bigger shaft pulley - but this will make your speed lower.
4. Be careful that belt drives damaged when installed on very small pulley. Dented belt or notched v-belt can be used for small pulleys.