As promised, I just included the first five sentences I wasn't sure of.
1) One day he got to the beach and saw it was covered with human bones. He realized that cannibals had eaten men on his island. He believed that cannibals ate other men because they thought it was natural.
2) He found a cave that was a perfect place for lightning fires. In the cave he found an old goat which was going to die. At the back of the cave there was a small tunnel. He went through it on his hands and knees till he came to a much bigger cave with a very high roof. He thought it was a perfect place to hide from cannibals.
3) In May of his 24th year on the island he heard a loud noise like a ship’s guns. He saw a ship through his telescope and lit a huge fire hoping they would help him. He realized it was a European ship but it wasn’t moving. When the sea was calmer, he took a canoe and went to the ship.
4) He couldn’t stop feeling excited by the idea of meeting someone. The ship sat on some rocks and there was a large hole in her side. All its crew had shipwrecked and the only thing alive was a dog. They must have died because of the violent storm. The best thing he found was two pairs of shoes and a box of money and gold.
5) The cannibals returned to the island two years after he found the bones. He decided to capture one of the them to be his servant. He was sure he could be friends with him.
All are fine.
The only one where I have a question (and it's a very picky one!) is in #1:
"He believed that cannibals ate other men because ... "
After the word "because," I was expecting you to give the reason why he believed this, not the reason that "cannibals ate other men."