Yes it’s good, though it’d be better if you used “Your sister and my sister are best friends, they do many things together” that (and) word doesn’t seem necessary. Hope this helped :)
Mary Shelley uses a multiple narrative in Frankenstein. A multiple narrative (sometimes referred to as an epistolary narrative) uses the voices of multiple characters within the text. Epistolary narratives can also use letters (such as Walton's four letters at the opening of the novel and the letters between the Frankenstein family) to detail parts of the plot and storyline.
