I feel your pain. Because I live on a court, this happens to me quite frequently (and usually by the neighbors boyfriend) I usually go and and talk to the neighbors. Short of that, you are at their mercy as it is a public street. What you can do is to watch how they park. If even an inch of their car is blocking your driveway, you can call your local PD (be sure to call the non-emergency line). They will send out a CSO who will measure to see if they are in your driveway. If they are, they will write a ticket. Of course the caviat is that turnabout is fair play. They can do the same to you.
Why not just park in front of their house?