There is no Alice-clothes-changing event, and no event which requires both Alice and Brenda. Not sure what anyone was thinking of there. The only event which requires two specific characters is the beach sex scene with Heather, which requires Jessica's help. The Heather-clothes-changing event (where she's picking a cosplay costume for the poledance) requires a second character, but it can be any of the other girls on the island.
For Yvette, when she's on night duty, go from the nightbar to reception at 23:30; if it doesn't trigger, go back to the nightbar, then go back to reception at 00:00; if it doesn't trigger, repeat process at 00:30. If it still doesn't trigger, don't be surprised; it might take a few days before it happens.
You're right, the search is a mess at this point. I think someone needs to start a Holiday Island FAQ thread and move all these discussions there; whoever posted it could include the walkthrough, and people looking for answers to questions would have far, far fewer posts to churn through to find them.