Technically, there's also Telethia to consider as well, though they aren't exactly sentient anymore and the fact that they're former High Entia isn't revealed until very late in the game, at which point killing them is viewed as more of a tragic necessity than a callous disregard for sentient life.
Yeah, so while interesting to note, I don't think it counts for this topic.
Hypothetically, you could say that they aren't actually killed, just given the Metal Face treatment off-screen (that is, beaten until they're unable to fight anymore, then spared). There's no concrete reason to presume that, but it wouldn't be the first time games have used such a pretense to explain random battles, and it would be more consistent with the characters.
Yup. It's unclear. Maybe you just disable them, so it's a minor example. The item they drop makes me wonder, but it has literally no purpose and you can't see a pic of what it even is, so who knows?