Allwyn/Alan/Horatio was born in 970AD and killed/turned by mistake in 1000AD. He's lived ten lives and there is far more to him and his character than the lieutenant in Miami. He is far darker and more evil than his Horatio persona would have everyone believe, but he keeps it hidden from everyone - except his boy - because he feels that his life is his own business. There will be more about his history as the story develops and not just how he came to know Greg House, although that will be the focal point in most of the history chapters.
Greg House was born in 1959 and turned in 1974 when he was thrown down the stairs by his biological father. He remained with his sire, Alan, until 1979 when he entered medical school. The rest of his past is more or less cannon with the show, the most notable exception being that he and Alan remained lovers until Alan bonded with Tim Speedle in 2004.
Tim Speedle was born in 1973 and turned in 2004 after being shot in a jewelry store. At the time of his turning and bonding with Alan - now living under the name of Horatio Caine - he'd known Horatio for three years and they had been dating for two. He was unaware of his lover's true nature until he was shot. He also knows the bare bones of Alan/Horatio's time and relationship with Greg House.
Eric Delko and Ryan Wolfe are also vampires and bonded. More about their story will come out in future chapters. Okay, feel free to rant and rave at me now. *snickers*