Can anyone approach a Don's Consigliere and request a meeting with the Don without another Don [even a lowly pimp Tattaglia....] vouching for them? Have I got a deal for you!

Also how do they approach the first Don -- How was Sollozzo able to meet up with Barzini / Tattaglia?
Was it because Barzini / Tattaglia were lower in the pecking order and Sollozzo was able to just front up and knock on their door not dissimilar to Roth's open house!

Why was Fredo carrying a Gun? Sonny never did Lucky! for Carlo....