How to deal with my fiances bratty twins?

I don't know what to do with these girls, they are such brats that I have a hard time wanting to be home when they come to stay with us. One is very much like her mother, thinks she is the **** and is a total leech, she is so up your that it gets very annoying and very nibby, then the other is hateful and mean. They both say stuff to friends and family that is totally uncalled for and embarring, I would my own child if he acted like theses two, but he is well mannered and would never say anything that would hurt someone else's feelings. They are both 9 and act like they are 5. What can I do?