Three things

My only human main is locked out too, but all of the cutscenes are in the strategy guides. And actually, it looks like most of the info we're looking for isn't even in the cutscenes anyways, they're from the dialogues of characters which isn't stored in the library, unfortunately.

For Morgant, in G3 Priest James mentioned that Esras ordered Redire to capture a human child, which made the Dark Lord come after them, and from this he reasons that Triona must be the ressurected form of Macha who just hasn't awakened yet, otherwise why were the Fomors so extreme over just one child? From this I think it's implied that Morgant was a Dark Lord before Triona's kidnapping, and we can kinda say Macha isn't dead. Dunno what ressurected but asleep would be equivalent to here.

For Nao, Duncan explains that Lia Fail's process isn't a Goddess inhabiting someone else's body, but instead the slow merging with a God/Goddess who chooses the body as a median. He then mentions that's also how Nao became what she is today. So it does look like Mari had to "become one" with some different entity to become a deity herself. But Duncan does confirm Mari's a "God-like presence" now.

Slight bit more info about Macha, she could control the psyche of her soldiers to make them fight as one, and I think it was mentioned that she could make her opposing army go crazy as well. Plus, she could read minds, so she knew that she was going to be betrayed one day, even though she chose to believe in love. That was from the information gathered from Emain Macha residents.

I think that's all I found...