I'm confused about the story from underworld: rise of the lycans?

I did watch the first two, but I don't remember too much of it. Can anyone please explain who the narrator was in the end when selene came up? Why was her grandfather in the coffin? And how did sonja give birth to selene when she died? Any summaries will do from those who know this series well. I'm sorry I'm confused I just want answers. Thanks for those who have patience with me.