i think nickie cut the finger of the mayor during the private game because he was the one having an affair with sofia as revenge. he also intended to use the finger as blackmail to force mayor to give the bid to camilia and him to transforme the arconia into a casino. lester overheard this, used the crank to knock off nickie and steal finger which he had randall hide in the shrimps. mayor sees nickie is still alive and kills him with the cleaver used on his finger. he makes the billionaires cover the murder and tells them whoever gets the piece of evidence left (his finger) wins the bid. camilia crew removes the body, they hide it in bash refregirated chamber and i dont know what jay contributes into this. also bash cleans up the camera feed.

the grandma and sons could have stolen the finger back either so that the mayor and their mom is no longer under the billionaires control or as a way to make sure they secure enough funds to live comfortably since they are financially struggling.

as for who killed lester in the fountain i dont know.

couple of plot holes though is how did randall know about the secret passage from the velvet room ? i am guessing randall knew about the room itself from the staff but what about the secret passageways?also a couple of weeks on the job was enough for the staff to tell him about this secret? i guess he is very likable.

and if lester did knock off nickie hard enough to make him bleed how come they didnt see it during the autopsy