Sometimes family is blood. Sometimes blood isn't family. Sometimes family isn't blood.
Make any sense?
I think the people in our lives who return our love and don't use, abuse, or take advantage should be considered family. Whether you share similar DNA or not makes no difference, in my opinion.
Today in class, my students had a discussion about adoption. I informed them after the discussion that I'm a big proponent of adoption, that my little brother was adopted, that my newest siblings are adopted. One student asked if I'd adopt internationally, or if I'd discriminate, and I said, "I'd adopt from anywhere!" Because to me, we're all human beings, and that qualifies us to be family.
Now, if you've got a blood relative who is a horrible person, I think you should have equal rights in considering them Not Family. People who say they have a moral obligation to blood are missing the point. And they're causing themselves a lot of grief in the process.
Life is too short to be manipulated and taken advantage of, all in the name of "family."
So I say, choose who you take on as your family. Make it the people who bring love and joy into your life, and screw the rest.