tests can accelerate cancer growth. if that is of issue when giving blood, i do not know.
i'd just be honest with your doc. you can insturct him to keep what you talk about between the two of you.
the odd's of only you being a match and nobody else in the famliy are slim.
if he can't use your blood, then they will get it from the blood bank. before my last operation, i donated blood to myself should i have needed it. but this being cancer, that's most likely not an option.
good luck to your father.