Sphink`s ridddle #2

Question: I have the same mum as somebody else,the same dad,the same birthday,the same age and the same sisters but we are not twins. What are we?

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?

Question: During what month do people sleep the least?

Question: When is 99 more than 100?

Question: What can be broken but never forgotten?

Question: Surrounded by life , yet life is its biggest enemy. But without life there is no need for it to exist. What is it?