Automatic update of duplicate activities in separate projects?

Hi all,

This is our situation:

There is one Master schedule (Project 1). There are three separate (P2, P3, P4). Project 1 consists of some unique activities and some activities identical to those in P2, P3 and P4.

Those activities in P1 are linked to the original activities in P2, P3, P4 by Start to Start logic. The intent is to manually update P2, P3 and P4. My question: is there a way to automatically update the same activities in P1 (because we want them to rreflect the same info)?

Thank you very much.