There was a 7-year gap between your GM and Francesca and Giuseppe's birth, so there could've been more children in there and possibly even another set of twins. There could've been more half-siblings, too, especially between 1909 and 1919, but I don't know how much your GM knew about them.
It would be very easy to check if there were any other Cina' births in Ribera between 1886 and 1891. It should only take a few minutes.
Edit to add:
I checked and there were no other Cina' births in Ribera in those years. Maybe they lived somewhere else temporarily.