One positive HIV test result means very little and should never be believed in this type of situation. Please get another test done from any reliable laboratory. One needs to be concerned only if both the tests are positive, one positive report can be a false positive which can often happen in the case of HIV tests. I do not know where you are, but the chances are that there is a VCTC (Voluntary Counselling and Testing Centre) near you. Go to any VCTC and get your father to have another test. If it is negative, forget about the whole matter. If is again positive, then consider the possibility of HIV infection.
Even if he has an HIV infection, remember that he needs love and care and not condemnation. HIV is not infectious to other people except through blood, injection needles and sex. There is no danger in keeping an HIV positive person at home even in a home full of children, sharing food, using the same utensils, bathrooms and bed. Also remember that ten years after infection, 50% people are still well and without disease.