The phrase "my father's son" can only refer to the speaker himself, since he has no brother. So the correct answer is the speaker's son.
Solve this puzzle
Erin reads an average of 20 books per year. She read 23, 17, 20, and 19 books in four different years. How many books did Erin read in the 5th year to make it an average of exactly 20.0 per year?