Do You Know Eachother?

I bet the other guy in my Spanish class was so confused. My sister, who is in that class, and this guy and I were doing a skit. My sister and I were having casual arguments, mainly playful. "Can we share a book", "Get your own book", "How about you say this line", "I don't want that line, you say it, my idea was better", and so on and so on. He saw us outside class, and asked if we knew each other. We said, yeah kind of, we're are brother and sister. He thought we didn't even know each other until the class. At least now he knows and probably understands why we have the interactions we do.