Final answer:
The sentence provided is already correctly punctuated and does not necessarily require changes. Dashes can be used in place of commas for clarity, similar to the provided examples.
Step-by-step explanation:
The sentence "Maureen's three sisters, Molly, Shannon, and Patricia, are all spending the summer at their grandmother's beach house." is already correctly punctuated. However, if clarification is the goal, dashes could be used in place of commas to avoid confusion, as in the example: "The cousins—Tina, Todd, and Sam—arrived at the party together." This punctuation style is particularly useful when the sentence includes additional information that might be complicated by the use of too many commas. It is important to ensure punctuation serves the purpose of making the text clearer and more readable to the audience. Using dashes in this way can help delineate additional information or asides that are not the main focus of the sentence.