I do feel for the guy but, if you don't get them a tow company will and he'll never see them again.
So what I would do is get them and don't forget all your documentation, including that from the person whom bought the house at auction, showing the person was given notice and time to remove the vehicles. This way you have proof that you did not steal them. After that I would try and make a deal for a vehicle as payment for the transfer and storage. I would do this because of guilt but you're helping him out because he will probably loose them all if not. He and a lot of others will try and make you feel guilty, but think how bad he will feel if he ends up with nothing. Terrible way to look at it and probably not right and I'm kind of on the fence about the guilt. Chance's are he hasn't gotten them because he has no place to put them. If they were mine they would have been out of there way before foreclosure, even if I had to park them in the street until I could figure something out. Pete