Great observations DC and TB, and I will take it a step further.
In a meeting like this it is totally inappropiate for anyone to
speak other than the two people doing the negotiating (imagine Al Neri telling Senator Geary "You're telling me that the only way we can move Klimgman out is if we pay you a bribe?). What this tells Sollozzo is not only that Sonny is hot for his idea, but that Sonny is hot to take over the franchise and is counting the days until Vito dies or relinquishes power.