its probably better to use different Movie Players in the same scene and trigger them according to when you need each movie to play. You can add Video Mixers or Selectors between Movie Players and your Projector(s) and trigger values to these using various methods, such as Envelope Generator, Trigger Delay or Comparator.
If you initialise the speed of each Movie Player to zero, it will not play until you trigger a value of 1 to it.