1) a.
"Him" is an object pronoun, and object pronouns typically occur in the predicate portion of a sentence. One tip on deciding whether to use him or her is to say the sentence without the "my brother and". Would you say: " I just found my favourite photo of he" or " I just found my favourite photo of him?
2) b.
"It's" is an abbreviation for "it is". Would you say: "The car is showing it is age"?
"Its" is used for describing an object's or animal's possession.
3) b.
The setting is absolutely vital to the reader's understanding of the story. The era of which the story occurs in can tell you about how the people acted, the laws at that time, what type of language they use, and any significant events. Without the setting, readers would be unaware of most details in the plot.
Hope this helps!