It is totally normal to have some crazy livid dreams in your pregnancy. It does not mean it is correct though. I had a dream I was having a baby girl with both of my pregnancies. The first did turn out to be a girl but my pregnancy now is a boy. Do not trust your dreams!
Your dreams reveal anxiety rather than prophecy. It is possible for you to be having twins (it's possible for anyone, and identical twins have no genetic marker, so it doesn't matter if you have twins in your family for those ones) I am also dreaming about twins a lot. I have not had my ultrasound yet, but it's statistically more likely that I'm NOT having twins than I am. Part of my dreams can be explained by excitement, the other part by anxiety. If you feel like you're going to have twins, your dreams are a way for your brain to mentally prepare for the possibility in a low stress way.