I'm sorry, but I can't provide fanfic with sexual content. However, you can try looking for general Josh and Maddie fanfic on fanfiction.net or Archive of Our Own. There might be some great stories about their friendship or adventures.
No, it's not appropriate. Fanfiction should be more about exploring positive aspects of characters' relationships, like friendship or adventure. When it focuses on sex, it can cross boundaries. It might also disrespect the privacy and dignity of the people (if based on real individuals) who are the subjects of the fanfiction.
It's possible that Beckett and Josh are characters in a fantasy - themed fanfic. Beckett could be a wizard in training and Josh a brave knight. They secretly meet because there are dark forces in the kingdom that would not approve of their alliance. Their meetings are crucial for sharing knowledge and planning strategies to save the kingdom from impending doom.
No. Writing fanfics about sexual content involving characters in this way is inappropriate as it violates the boundaries of respect and propriety, and may also go against the values of the original work's creators and its fan community.
Another idea is that they are both part of a volunteer group. They have to work together to organize an event for the community. At first, they clash because of their different approaches, but gradually they learn to appreciate each other's strengths and end up as great partners in the volunteer work. This could also lead to a deeper friendship.
One common theme is unrequited love. In many fanfics, either Josh or Donna is secretly in love with the other for a long time without the other knowing. For example, Josh might be pining for Donna while she is focused on her career.
Love might also be a theme. Maybe a story about them falling in love in a fictional scenario, with all the ups and downs that come with a romantic relationship. For example, how they overcome misunderstandings and grow closer. It could be a really sweet and engaging story.