PF: One battery block, one IR receiver, two motors on same port
You can attach (stack) more than one motor on the same connector (red or blue) of PF IR Receiver to control them at the same time. This is exactly what is being done in 9398 set, for example (although it uses V2 of PF IR Receiver). They will be spinning in the same direction with a push of a single button. If you need to reverse the rotation of one of the motors Pole Reverser comes to the rescue.



At this point of time there is no option with Powered Up to control both ports on the same receiver with a single button. Each port accepts just one motor, so you cannot make both motors attached to same receiver spin at the click of a single button - you need another receiver (on the same channel as the first one) for second motor to be controlled simultaneously.

Edit. Stacking motors on the same PF port/connector doesn't provide unlimited power and has its limit. Usually, couple of motors doesn't cause overheating protection to kick in, unless they are strained.