The only people I'd be sure he couldn't kill are Hideyoshi and his Fiance, Shannon. I'm not just talking about the Headship test in game 3
[16] where he outright says he can kill them all. George is calm and collected he's good at smoothing things over and directing conversation to the point where you might forget you were even talking about something uncomfortable just a minute ago. In certain scenes he's shown to be manipulative and says in his narration that he likes to bully Shannon that exposes that nature (though in a loving way)
[17] . It wouldn't be unusual for him to be able to manipulate people into being an accomplice in murder in cases where he can't do it by himself in fact he's the only family member specifically shown to be ordering the servants for selfish reasons.
[18] The only thing almost anyone else orders them for is delivering tea and doing chores. So it's possible for him to take advantage of rank and a furniture complex to gather accomplices if he doesn't have to bribe them. Here's an example of were he might by signaling an accomplice.
[33] They don't even really need an order to follow him as long as they believe it is his will
[19].(this kind of influence is also thought of as a possibility in Higurashi in Shion's TIPS about the Sonozaki conspiracy) In game 1 Eva implies something along the lines of “that if 19th person does not exist that means someone is manipulating people to murder (most specifically the servants) and George, ironically fits the bill in her theory about the culprit.
[20] In this scene he's called a new master of the servants
[21] Even more than that he thinks like a king using Hideyoshi's stories from the Sengoku era and Eva's monarch like attitude to create his own philosophy on life.
[22] At the same time he's shown to be possessive of Shannon
[23][32]. As noted by Oliver the metaphor used in reference to George's wedding ring that it's meant to say “this woman is mine” is very similar to the description to Erika's specially made ring for Battler in game 6
[24]. It's also emphasized in that same episode that George has no interest in becoming the family head
[25]. So I can rule that out as a motive, honestly though I don't think it would've made sense as a motive for murder in the long run anyway. He wants to create his own business empire, and his own family
[26] with the way he talks I don't think he has any attachments to this family right now I don't think he'd have a huge problem getting rid of them, but I don't know about what Shannon would think. It's said that he's well on his way in the business world, he's very prepared and I've suggested it's possible he had someone he knew like Okonogi
[27] to pull some strings and fill the safety deposit boxes with illegal/yakuza money. Like Genji, maybe Okonogi owes him some kind of debt or maybe George promised him financial backing in the future. It could explain the 'world peace' thing in the game 6 tea party. Furthermore George was prepared enough to know that the Typhoon was coming and change his schedule, and this level of preparedness is necessary to set up a serial murder scheme like this
[28] not only that I'd say it suggests he has some sort of big business responsibilities since he's prepared to go back on monday. The TIPS describe him as “an Affable young man who is loved by everyone in the family”
[29]. It'd be totally unexpected for a
“nice guy” like him to be a mass murderer.