To sync multiple videos over multiple players you will need to perform the following:
1. The players will need to be on the same network so they can be visible and synch from each other.
2. The Playlist will need to be the same length. (They don't need to be the same name but the same length will make sure that they start at the same time and end at the same time).
3. The players need to be the same model make. If you have different spec players then the sync will be out as some players will be faster then others.