So I was doing runs, buying Iron Ingots and leather strips when a dragon attacked Riverwood for like the 1000th time. Usually Faendal and Avlor die and I just resurrect them as normal, but this time both Avlor and Sigrid died. And even though I resurrected them both, Dorthe's dialogue hasn't changed; talking about her parents dying and I can adopt her. I've tried some character resetting console commands that I've seen lying around the interwebs but none of them work, at least on her. Is there a way to make her realize the people sleeping in her house aren't ghosts but real people?

Ain't gonna work, the script ran. Same as when you fail a quest, resurrecting the quest giver won't work. Script for failure is there, but there's nothing to reset it if they get alive again (because they weren't meant to get alive again).

Does the same happen if only one dies?

Like, Avlor and Dorthe have some dialogues about her becoming a blacksmith. If Avlor dies and is resurrected through the console commands, would they still have those unique dialogues?

The dead are meant to stay dead. It's programmed that way.