The correct answer is D. No error.
The sentence “Neither he nor his father is interested in joining the party” is grammatically correct. The word “neither” is used to introduce the first of two negative clauses, and the word “nor” is used to introduce the second. The two clauses are joined by the conjunction “is interested in.” The sentence is in the simple present tense, and the verb “is interested” agrees with the subject “neither he nor his father.”
The sentence could be rewritten as “He is not interested in joining the party, and his father is not interested in joining the party.” However, the original sentence is more concise and easier to read.