One idea could be that the Reaper loses his scythe and Billy and Mandy have to help him find it in the Underworld. They encounter various strange creatures along the way.
I don't have enough details about Georgie and Mandy to share their full story. It could be a story about two friends, siblings or even two characters in a fictional world. Maybe they had an adventure together, or overcame some difficulties in their relationship, but without more context, it's hard to say.
I'm not sure specifically what the'mandy and the kids story' is about without more context. It could be about a woman named Mandy and her experiences with some children, perhaps she's taking care of them, teaching them, or having adventures with them.
One common theme is friendship. Despite their differences, Billy and Mandy's friendship is always a central part of the fanfics. Another theme is adventure. They often go on various adventures together in the fan stories.
I'm sorry, I don't actually know who Mandy Monroe specifically is. There could be many people with this name. Maybe she is an ordinary person living a normal life, or she could be a local figure in a certain community.
The main characters are obviously Mandy and the kids. But without more details, we don't know how many kids there are or what their individual personalities are like.