Probably depends on where you live. In general there’s no obligation for them to do anything if it’s not on public property or actively causing a safety hazard. OP is from California where nothing is straightforward legally. Towing companies may also not want to deal with any headaches depending on the local regulations and may not take the job unless they can get something out of it (payment or ability to take possession of the vehicle).
What I want to know is why hasn’t he shot it yet? I mean, this is America, the van is on his property, and it’s clearly up to no good. Sure, it could be a broken down POS just like they say; but that might be just what the Amazonians want him to think and as soon as he gets complacent, the two-dimensional kick-murder team hidden beneath the passenger side floormat will unfold into real space and cancel his returns with maximum prejudice. Don’t you feel threatened? I feel threatened… Ma! Get the gun! There’s ground that needs standing!