I am defedant in my sons custody case.The Judge granted me custody of our son.The -Plaintiff - mother requested a psychological evaluation of our

It depends on what the judge has indicated and why the psychologist wants to come to the house.  It is likely that when the judge ordered the evaluation the judge did not anticipate the doctor coming to the house, because then it involves you, your house, how your son interacts there.  I'm not sure why the doctor has to do that and i think you are entitled to an explanation, and that your son should be seen in the doctor's office first.