I think Aiello would be too strong and assertive for Fredo/Freddie, and Pollard would be too goofy.
I'd reach into "Goodfellas" because Scorsese also was a master caster of Italian-Americans. My choices would be Johnny Williams (Johnny Roast Beef) or Tony Darrow (Sonny Buns), both of whom played occasionally clever but weak characters.
Ntra la porta tua lu sangu � sparsu, E nun me mporta si ce muoru accisu... E s'iddu muoru e vaju mparadisu Si nun ce truovo a ttia, mancu ce trasu.