The answers to the questions would be the following ones:
1) The underlined pronoun represents the objective case. That is, your answer would be option B.
2) The underlined pronoun that is in the possessive case is "hers". That is, your answer would be option C.
3) The correct form of the pronoun to replace the underlined words would be "they", that is, option A. You need a nominative case pronoun for the subject of the sentence.
4) The correct pronoun to complete the sentence below is "him". That is, your answer would be option C. In this case, "than" functions as a preposition that takes that pronoun as the D.O.
5) The correct pronoun to complete the sentence below is "her". That is, option A is the right answer.