Final answer:
In the provided sentences, 'her' is an indirect object and 'them' is an object of the preposition.
Step-by-step explanation:
In the sentence "Aunt nan took the message for Walter and her," the word 'her' functions as an indirect object. This is because it receives the benefit of the action being done, which is the message being taken by Aunt Nan for Walter and her. In the sentence "We joined Mark and (them) on the observation platform," the pronoun 'them' is the object of the preposition, as it is the object of the preposition 'and' and follows it within the sentence structure.