Yes they are edible, but various critters got most them before we ever did. Eventually we planted fruit trees instead and had much better success.
More info:
http://www.scs.leeds.ac.uk/cgi-bin/pfaf/arr_html?Prunus+besseyi&CAN=COMIND
More info:
http://www.scs.leeds.ac.uk/cgi-bin/pfaf/arr_html?Prunus+besseyi&CAN=COMIND