Old Vampire books from before 2004

[Joshua]

I remember reading this book back around 2002-2004 after I bought a copy from the dollar tree near my house. It was about vampires where the father raised the son who is immune to sunlight and the mother raised the daughter( I think she was more of a human girl than vampire but I'm not 100% on that) with help from a crippled man servant. i remember the father took the son away for either study of his abilities or because he was a threat to his sister.