First that isn't Fischetti.
Here's pic of the Fischetti brothers while Charlie was alive (died early in '51)


We know Fosco's pic in no earlier than '56 ('56 Belair in the pic)

Joey(right) is already balding and paunchy.

Next, we don't necessarily see every one in attendance, just a bunch of guys around one picnic table. Anyone else could be milling around.
Third, don't assume that this is some kind of meeting, it may just be a picnic.

In '56, Joe B held the last July 4th party at his home. In '58 they started holding them at Jackie the Lackey's house.

Perhaps they held the 1957 party at a picnic grove.
As such it was a social event and anyone who didn't have a contract out on them may have been there.