I remember that . . . . . . . . bought the fruits from . . . . . . . .

Personal pronouns are used to indicate people while possessive nouns are used to indicate something belongs to someone. 'Them' and 'they' are both personal pronouns but the difference between them is that 'them' is an object pronoun whereas 'they' is a subject pronoun. 'they' can be used with the subject 'us'.