The first car they took was Deepak's (rumored to be Joran's) Joran does not own a car. Deepak own the silver Honda. Daddy & Mother VDS car's were took just last week. Now does it make sense?
I still think you are very close to the possible truth. But I also think Natalee was drunk...and her friends knew it, and she introduced herself to Joran like the two girls insisted she did. I do not think they were preying on her as it was first believed. Nor, was she involved with him, and having a summer fling (which would have been understandable).
Perhaps with the 3 fellows it was, after all, a really bad accident - and Daddy has tried to cover it all up, by involving some seemy characters to assist.