How can a father leave his mortgaged home to his son?

He should speak with an estate planning attorney and consider using a revocable trust. Issues at the meeting should include reviewing the promissory note and deed of trust to determine if is assumable, ,etc., as well as discussing a plan for the balance of his estate and handling of debts and other obligations. This is opinion is solely based upon the facts presented in the inquiry. Additional facts may be important and may change the analysis. If you are uncertain, seek legal counsel.