I think there is a leak of current going back to the LED from the Arduino?
Make sure the Arduino is configured to be an input, also wire not directly to the LED as this is not enough of a signal to register as a logic 1 but to the resistor feeding the LED. Finally make sure there is a common ground between the detector circuit and the Arduino.
So I can make them do different things, but when i write the command one comes after the other and therefore they dont move at the same time
Its a matter of your code, you will find that is what you are telling it to do. It's not so much the command but how it is structured in your code.
So set one motor going with a digital write 8 & 9 then the other to 6 & 7 and they will both go at the same time.