Several Plot Holes?

Now I may be wrong about these and I would love someone to explain it to me, but there's several things about this movie I just don't get..

1. Chris, Marty and Philip weren't trying to frame Vincent for MURDER, so what exactly were they trying to frame him for? Being present during a suicide? Is that a crime, and is it worth the risk of this elaborate obstruction of Justice?

2. Presumably by the end of the film the police know EVERYTHING that happened, so surely all four of these guys, save possibly Vincent, would be in jail.. They tried to frame a man..

3. Is Phillip just supposed to be stupid enough to think that cutting a girls wrist like that hours after she dies from an overdose will look like she did it herself?... I guess he is..

4. What exactly was on those dvds the cops had, Vincent sleeping with all their wives? That would incriminate them wouldn't it..

5. Was that supposed to be Anne they saw over the balcony leaving the building after they got buzzed from the estate agent? I'm sure this isn't a plot hole, just something I didn't understand..

Can anyone help explain this stuff to me?