The possessive form for the Marx Brothers is the Marx Brothers'.example: The Marx Brothers' nonsense is still popular today..
Groucho
In the ideas of Karl Marx
No.
Marco Marx of the Marx Brothers
Movies about the Marx brothers have not been made because they parted ways with the Paramount.
Marx Brothers
I can actually understand why you might think that the Marx brothers were Italian, since Chico Marx had what seemed to be an Italian accent (although Groucho, Harpo, and Zeppo didn't). But no, they were not Italian. They were Jewish-American. Why then did Chico have that Italian sounding accent? Well, they were comedians, just trying to be funny.
No. However the Marx brothers did star in "A Night in Casablanca"
No.
nope
They were Jewish.