Haha, yeah, I had a similar idea about Kinzo's apperance in Episode 4. Namely, if Genji and Kanon had brought Kinzo's PORTRAIT and read his will, then Kinzo appeared in the dining hall and ordered murders.
The rest of this is a long winded supposition. I don't claim any of it's true, I'm just following the thread of logic
We then assume that Gohda and Kumasawa are in on the murders, and Gohda executes the 6. Perhaps Kumasawa had drugged their tea, and the rest fainted *except Kyrie and Nanjo*, who are also in on the deal. They then transport them to Kuwadorian, where Kyrie and Nanjo are locked up as well.
Nanjo says he does not know of a drug that can make people faint like that. Kyrie asks Gohda and George for the time. That way, Kyrie only has to say "My watch says the same" and people are then lead to believe that no time had passed, despite the fact they had winded the clocks back.
When talking about the Test on the phone, Battler's deceleration of war is heard by Kinzo, but Kinzo's response is not heard by Battler... Namely because Kinzo didn't exist, so Kyrie heard Battler's deceleration herself However, Battler is also in on this, so this point is moot.
Gohda and Kumasawa are locked within the shed. However, after Jessica and George leave, Battler murders Maria with poison in her tea. He then goes and unlocks Gohda and Kumasawa, who proceed to murder George and Jessica. Jessica sees George enter the garden, hears a bang, and knows he's dead. Gohda then enters the room and shoots her. She does not call Battler.
Battler himself goes to the Kuwadorian, and pretends to lead a jail break. He then kills the survivors, and Nanjo. Kyrie flees to the mansion, knowing she's been betrayed, and Battler kills her then too.
Gohda had been in the boiler room, where he was disposing of Kinzo's body, and rigging the mansion to explode, unbeknown to Battler. Battler shoots Gohda and Kumasawa (the guns, btw, came from Kinzo's collection), and hangs them back in the shed.
Finally, Battler goes around, poking and prodding the bodies, and destroying the validity of the crime scenes, as an excuse for later. He spends a day on the island before the boiler explodes, killing him, along with destroying the set up.
Obviously there's some insane flaws in here, such as who orders the test... but that could have been done through letters.