So let's say you pay the new owner, and he lets you remove all of the cars and you put them safely away in storage far from the old owner. You still don't have titles to the cars, in fact the old owner still has titles and is rightfully the owner of the vehicles,right?
You would need to file for abandon titles for all of the vehicles, in the mean time, the old owner reports them stolen or something? Sounds like a lot of BS. I would talk to a lawyer, or someone who knows the laws pertaining to property left on a foreclosed home, you don't want to be out 10's of thousands of $$.
It sounds like the old owner is SOL, but you want to be sure that what you are wanting to do is 100 percent perfectly legal, IMO.