Ferrari is not part of Fiat.
Battista Pinin Farina that designed the Ferrari also designed
the Fiat 124 spider, lancia
The company itself have no relation other than using the same
person to design the cars.
Battista Pinin Farina was employed as a designer by a lot of car
makers like Maserati, Rolls-Royce, Cadillac, Jaquar, Peupeot, Alafa
Romeo, but there many more.