Stating that I own Harry Potter (or any of his friends or enemies) could get me in trouble, therefore I will refrain from doing so (especially since this comes nearly literal from the book :D ).
The opinions of the Dursleys are not identical with my own!
Mrs Dursley's sister
The Dursleys had everything they wanted, but they also had a secret, and their greatest fear was that somebody would discover it. They didn't think they could bear it if anyone found out about the Potters.
Mrs Potter was Mrs Dursley's sister, but they hadn't met for several years. In fact, Mrs Dursley pretended she didn't have a sister, because not to long after the dead of her husband Mrs Potter had moved in with her girlfriend.
When she was still a teenager Mrs Dursley thought that her sisters bisexuality was just a phase and after all, didn't her marriage to this Mr Potter confirm this theory? The Dursleys knew that this marriage had resulted in the birth of a child but luckily they had never met the kid ..., or the girlfriend. They shuddered to think what their neighbours would say if they knew. Even though Mrs Dursley tried to think about her sister as little as possible, she sometimes couldn't help but wonder if perhaps wizards thought differently about this kind of inclination?!
I hope you liked this little drabble. I came up with it when thinking about how the first HP book was published in 1997 but Civil Unions only became an option for same sex couples in the UK after 2003.