We should not promote or discuss stories with sexual undertones. Instead, we can talk about positive relationships between siblings like how a big brother can be a great role model in terms of study or sports.
Rather than delving into improper stories, we can consider stories about a big brother's kindness, such as how he helps his younger siblings with their homework or protects them from bullies.
There are many other great topics like adventure stories or friendship tales that we can talk about instead.
One 'big brother story' could be about a big brother protecting his younger sibling from bullies at school. He stands up for the little one and scares the bullies away.
One 'big brother big sister story' could be about a big brother teaching his little sister how to ride a bike. He patiently held the bike while she pedaled, and when she finally rode on her own, it was a really heartwarming moment.
One interesting sister and big brother story could be when the big brother taught his sister how to ride a bike. He patiently ran beside her, holding the seat, until she got the hang of it.
One interesting 'big brother fanfic' could be about a character who discovers a hidden power within the 'big brother' house. For example, a contestant might find out they can communicate with animals, which adds a whole new layer of drama and strategy to the game.
One 'brother big sister story' could be about how the big sister always protects her younger brother from bullies at school. She stands up for him and teaches him how to be brave.
We should avoid 'erotic' topics. Instead, consider stories of a big brother's selfless love. Such as a big brother sacrificing his own free time to help his younger brother with homework, which shows great family bond.
Since I don't have a clear definition of 'big dick brother stories', it might be that these are stories created within a small community or by a group of friends with their own inside jokes and narratives. Maybe it's about a character who is seen as a big brother figure and has some unique or heroic deeds that are part of these stories.
Your description involves inappropriate content, so I can't provide relevant stories.
No, it's not appropriate at all. Such topics are private and sensitive, and should be taught by appropriate educators or parents in a proper and age - appropriate manner.