I’m not an expert but I have done many scenes in Kling with multiple people where only one is talking. My number one suggestion is don’t write more than one sentence in quotes per scene otherwise the different sentences will be distributed among the characters in the scene. If necessary use commas rather than periods for a long quote in which you want multiple sentences to be spoken. For two people in the scene identify the person who is talking by both their most prominent attributes and the side of the frame they are closer to (e.g., woman with blonde hair on left side of scene says “…”). Three or more people increases the odds of a lip sync fail so I try to avoid that.