Syntopic reading is what you need to do. Check the PhotoReading book page 112 for a layout of a master mind map for syntopic reading.
It helps you to pull out the relevant passages from each book with the necessary details, page number, passage, author book and quote visually available and linked to your statement of purpose in the center, ready for citation.
While there is only one stem and perhaps 2 passages you can add more as is relevant. Note you don't need to write the whole quote just enough so that you can find it again, since your write the page number next to the quote.
Alex