I love sentences like this. No sarcasm. Of all the types of Italian phrases I've translated in Duo these are my favorites. In English we just sort of barf out "It's my uncle's car". There's a sort of rhythm to the Italian phrasing.
"My uncle's car is more little" not correct?
We don't say "more little" in English.
Smaller or littler, though "littler" sounds a bit childish.