X2If you keep the dog confined to a safe place to have her puppies, there's a chance the owners may complain that you "stole" their dog.
But if you set up a safe place where she can freely come and go, and she chooses to have puppies there, then it's really their fault for not keeping the dog home.
And depending on how observant the neighbors are--if they say she's not pregnant, and if she has the puppies on your property, they may never even know about the puppies unless you tell them. (Whether to tell the neighbors would be a decision for yourself and your parents.)
I wouldn't tell them if they don't notice. Those sort of people don't need to have responsibility over any animal