Think of them as two fighters in a boxing ring. One you are for and the other is going to punch him out cold, if he can. In a story, the same goes for the two that are at odds with each other.
They both, in some way, work against each other.
If antagonist did not want to harm protagonist, he wouldn't be antagonist. His opposition to protagonist is what makes him antagonist.
The antagonist is the opposite to the protagonist.
For that matter, who is the protagonist of A Midsummer Night's Dream? Oberon? Bottom? Lysander? Hermia? It is not a play which lends itself to analysis using the protagonist/antagonist paradigm. The best answer is simply that there is no single Protagonist or Antagonist in the play. In every scene, different characters balance and contrast with each other.
Generally, yes. The PROtagonist struggles with the ANTagonist (think "PRO" and "ANTI") during the conflict of the story. In some stories, the two resolve their differences and combine their efforts to solve the crisis.
Brutus is the protagonist, Antony the antagonist.
The protagonist is Flik the antagonist is Hopper
The protagonist is Thor the antagonist is Malekith
the protagonist is Penny the antagonist could be her dad or sister
the protagonist is Stella and the antagonist is joe and paton
tho protagonist is jenna and the antagonist is micheal.
Antinous is an antagonist.