Riddle #59

Question: What relation would your father's sister's sister-in-law be to you?

Question: What do you get when you cross a witch with sand?

Question: What do you call a sad bird?

Question: What kinds of balls do dragons play soccer with?

Question: What can be broken but never forgotten?

Question: People see through me, but none pass through without killing me. I can be anywhere, and can be seen double or single. What am I?