To try to determine "who's who" in an aerial combat with several claims is most important to have copies of the individual mission reports for that day.
Have you got the one of your grandfather (and eventually of the other claiming pilots)?
You should also try to get in touch with the Mr. Giancarlo Garello, the Italian researcher who studied in-depth that combat while writing his book "Centauri su Torino", published in 1998 by Giorgio Apostolo Editore in Milan.
To try to get in touch with him, contact the publishing house (
http://www.apostoloeditore.com/Home.htm ) by e-mailing them at:
info@apostoloeditore.com