There are some favoritism shown in Hollywood. Sometimes, this is known as nepotism. Nepotism is when favoritism is shown to certain people in order to either get or keep a job or because there is more pay for that person based on being friends or family with the members of the producers or directors of the movie.
I believe in some cases nepotism plays a part, but most likely it is not done for the key major parts in the movie. The director wants this movie to make money and it is very important that the correct actor or actress can play the part. Otherwise, the movie loses money and the director may have trouble finding more work. However, for small minor parts, the director may hire a sibling or parent in the movie.