On circumstantial appearance, I can see why you ask. I do not know how that would be resolved should circumstances ever make the question pertinent. I suspect that should the circumstances arise some people may pose the challenge publicly! I am sure that had the DNA test been around in the past the issue of succession may have been more interesting.
Prince William is second in line to the throne, Prince Harry is fifth in line.
Currently it is Prince Harry until William has a child
Prince William will get the throne, since he is older and therefore has a higher place in the line of succession.
Prince Harry is currently Fifth in line for the throne. If Harry takes the crown but doesn't have children, he would be succeeded by Prince Andrew.
Prince Harry, after his brother, Prince William, who is after his father, Prince Charles.
Currently, Prince Harry is third in the line of succession to the British throne, behind his father Prince Charles and his older brother Prince William.
Harry has not given up his right to the throne, he is currently fifth in the line of succession.
William is older, and so ahead of Harry in the line to the throne.
Prince Charles, Prince William, Prince Harry, Prince Andrew, Princess Beatrice of York.
If you're talking about the line of succession, then if Prince William became king, but died without fathering an heir, then his brother Harry is the next in line for the throne.
Prince Harry is currently fifth in line to the throne so it is very unlikely that he will become King, but not impossible.
Prince William is second in line for the throne, after his father Prince Charles.