The correct option is D NO CHANGE
We use 'eldest' in reference to family members, hence the underlined words is correct, and option D is correct. Option A is used in reference to people outside the family, or even things, hence it's incorrect. Option B is a comparative, which is used when two people are compared. The sentence has more than two people, hence option B is incorrect. Similarly, Option C is a comparative, and used when the nouns are not related, hence it's incorrect.