Two characters on the same scene: 1 or 2 sound files?

[Telemacus]

I can't quite recall watching a video about lip-synchronizing where there's more than one character.
What's the recommended approach? like do you import the sound file for one of the characters first, do all the lip-synching and then do the other? or do you actually create a sound file with the 2 characters speaking and then do the lip-synching?

[slowtiger]

2 separate sound files and dat files.

[Telemacus]

Thanks Slowtiger!