Yes, they are brothers.
No, there is no relation whatsoever. Does this mean you think all Smith's are related, and all Johnson's are too related.
Casey Affleck is married to Joaquin Phoenix's sister, so Ben Affleck is not directly related to Joaquin Phoenix.
Casey Affleck is married to Joaquins Phoenix's youngest sister; actress, Summer Phoenix.
He is one of the most famous Hollywood actors and directors.