I'm German and I'm living in France but I was born in Italy (Sardinia) and my father's family is Italian. There is a whole village in North-east Sardinia (San Teodoro) where almost 50 Fideli live. As my parents were not married, my name isn't Fideli, but my father and his parents (both born Fideli) and the whole family is called so.
If it can help... I wonder if it's the same family. I know that the ancestors came from Toscany (Italy).