Just get the citations of each document from the Scopus database, export the results into two files, and write a Python script that does a set intersection. You can generalize this to any files.

You can export the Scopus results to .csv files, and then use the `csv` python module to read the files. You can then have the set operation based on the title of the articles (even though I would also export the DOI and use it). If you know how to program in Python, writing this script shouldn't take you more than one afternoon.