Riddle of the Sphinx 2

Question: There are two sisters: one gives birth to the other and she, in turn, gives birth to the first. Who are the two sisters?

Question: One day a man broke his leg. When he was sent home from the hospital he had to use a wheelchair. The doctors told him he could not go up stairs. When the man got home he realized he had stairs to get into his house on both sides. The man saw his neighbor, the doctor who x-rayed him at the hospital, getting out or her car. The man asked "can you carry me up the stairs?" The woman replied "no." Why?

Question: My thickness is no more than a few centimeters, yet my depth can span to infinity. Although mundane, I intimidate most animals. When in my presence, you will inevitably follow me. What am I?

Question: Some people peel my skin some people don't, you eat me nevertheless, with or without, what am I?

Question: What tastes better than it smells?

Question: What goes in the water black and comes out red?