The civilization of walls

Question: Pretend walls have their own civilization. Each wall is a different country with different culture. One wall has its own animal, one wall has its own nut, and one wall has its own street. What are the three things the walls own?

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

Question: During what month do people sleep the least?

Question: When is 99 more than 100?

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: The more you add, the less it weighs.