If we understand your question properly, you short sold the house to some unrelated person or third party. If so, then so long as the transaction was an "arms length" one with no collusion between you and the buyer, then you--and your short sale--have nothing to do with any subsequent sale by the person who bought from you, and he can sell to anyone he wants, including your son. You have no liability or risk for what an independent person does.
The Answer(s) provided above are for general information only. The attorney providing the answer was not serving as the attorney for the person submitting the question or in any attorney-client relationship with such person. Laws may vary from state to state, and sometimes change. Tiny variations in the facts, or a fact not set forth in a question, often can change a legal outcome or an attorney's conclusion. Although AttorneyPages.com has verified the attorney was admitted to practice law in at least one jurisdiction, he or she may not be authorized to practice law in the jurisdiction referred to in the question, nor is he or she necessarily experienced in the area of the law involved. Unlike the information in the Answer(s) above, upon which you should NOT rely, for personal advice you can rely upon we suggest you go to AttorneyPages.com
and retain an attorney to represent you.