I think it’s natural for a dog to bark at people that he doesn’t know. Strangers. You wrote that your daughter isn’t really crazy after him, so I guess that he feels that, and that’s the reason he acts like it.
Emm… and the same as for your neighbor: he doesn’t really know her, his owners were gone, so he was protecting himself. After all he is a dog, not a person. I doubt he understand things like where you, the person who take care of him is. He probebly felt alone and confused because all of the sudden another lady was taking care of him.
Who can blame him??