The pronoun "who" should be replaced with "whom" in the following sentences:
- "Who wants to help clean the pool so that it will be ready when summer begins?" - should be "Whom wants to help clean the pool...?" (though this is grammatically awkward, so this may not be the best example).
- "Who do you think should be the next president of the science club?" - should be "Whom do you think should be the next president...?"
The other sentences use "who" correctly as they refer to the subject of the clause.