5. he is my … brother, but he is not as smart as i am. a) older b) elder c) the older d) the elder 6. this month i've read two books: the lord of the flies and brave new world. i liked … much more. a) the latter b) the latest c) the later d) the late

5. a) older - просто как прилагательное
6. a) the latter - Пояснение: 

Use latter to refer to the second of two persons or things that have been mentioned. When more than two have been mentioned, use last.
For example:
He preferred oranges to apples, because the latter were not as juicy.
He saw Leathal Weapon 1, 2, and 3 and liked the last one most.