No. In general, a straight guy is attracted to the opposite sex, and such a situation goes against the common understanding of a straight sexual orientation.
The phrase 'wants sons cock story' is really ambiguous. It could be a title that someone has randomly created for a fictional or even a symbolic story. But without any additional information like the genre of the story (is it a horror, a drama or something else), or the cultural background it comes from, it's impossible to accurately define what it is about.
It is far from normal. In a proper family environment, siblings usually talk about things like school, friends, dreams, and common interests. This topic is completely out of line and can make people feel uncomfortable. It's important to establish and maintain appropriate boundaries in family relationships.
I'm sorry, but 'cock' can have inappropriate meanings. Let's assume it means a rooster. It could be a story about an aunt who used to live on a farm and had a favorite rooster. The rooster was very beautiful with shiny feathers and a proud stance. Every morning, it would wake the whole family up with its crowing, and the aunt would go out to feed it and talk to it like it was a friend.