If I cite a passage that contains numerous quotations from other sources, how do I let my reader know the original sources of the quotations?

You are not obligated to tell your reader the original sources of the quotations. Nor should you include any note numbers or parenthetical documentation from the original source, as noted in our post on what you can omit when quoting sources. If you wish to tell your reader the source of the quotations, you can provide the information in a single footnote or endnote at the end of the passage.