Definitely the Potter family. Harry Potter himself is a central figure, and so exploring his ancestors like his father James Potter and his grandparents is very common. The Weasley family is also popular. With so many siblings and their parents, there are a lot of family relationships to play with. And of course, the Black family. Their family tree is filled with complex characters like Sirius Black, and fanfiction often delves deeper into their dark past and the family's influence on the wizarding world.
The Malfoy family is often explored in family tree fanfiction. Given their status as a prominent pure - blood family, there's a lot of scope for looking at their family history and how they are related to other pure - blood families. Another one is the Lovegood family. Luna Lovegood has such an eccentric personality, and exploring her family tree can reveal more about the unique quirks of her family. Also, the Dumbledore family. Albus Dumbledore's family has a lot of mystery, like his sister Ariana, and fanfiction might try to piece together more about their family story.
Harry Potter himself is often included. He's the main hero of the original series, so it makes sense. Hermione Granger is also a common choice. Her intelligence and strong - willed nature make her an interesting addition to a harem. Ron Weasley can be included too, though perhaps less frequently. And then there are characters like Draco Malfoy. His complex personality can add a lot of drama to the harem dynamic.
Harry Potter himself is often written in these types of fanfiction. He can be either the 'little' or the 'caregiver' depending on the story. Hermione is also a popular choice. Her intelligence can be used in different ways in the DDLB relationship, like being a very nurturing 'caregiver' or a 'little' who is learning a great deal. Ron Weasley is another one. His loyalty can be a big part of the relationship dynamics.
Hermione Granger is often a character that is transformed in these fanfictions. She's a very popular character with a strong personality, so seeing her in a different gender role can lead to all sorts of interesting plot developments.
Harry and Hermione are often swapped. Since Hermione is such a strong and capable character, it's interesting to see her in Harry's role. Also, Neville and Harry are commonly swapped as Neville also has the potential to be a hero.
Harry Potter and Sirius Black are also paired quite often. Sirius was a very important figure in Harry's life. In slash fanfiction, with Harry being dark and powerful, their relationship can take on a different meaning. Sirius's wild and rebellious nature can be paired well with Harry's new - found power and darker side, creating a relationship that is full of passion and a sense of freedom.
One under - explored character could be Godric Gryffindor. Since the Potters were in Gryffindor house, there might be a deeper connection through their lineage. Maybe there are some long - lost teachings or powers that are passed down from Gryffindor to the Potters. Another could be Rowena Ravenclaw. There could be some intellectual or magical knowledge that has been passed down through the Potter lineage that has its roots in Ravenclaw. And the third one could be Helga Hufflepuff. We could explore if there are any values or skills from the Hufflepuff lineage that have somehow found their way into the Potter family over the generations.
Harry and Hermione are very commonly switched. It's probably because they are two of the main characters with very different personalities. Their friendship and the contrast between their skills and abilities make for an interesting body - switch scenario. Another common pair is Harry and Draco. The good - guy - bad - guy dynamic creates a lot of potential for drama and exploring different perspectives when they switch bodies.
Andromeda Tonks is a character that is getting more popular in Black Family fanfictions. Her choice to marry a Muggle - born and break away from the Black family's pure - blood ideology is an interesting aspect. Fanfictions can explore her life before and after this decision, and how it impacts the Black family as a whole.
Luna Lovegood can be a popular character in such fanfiction. Her unique view of magic can add an interesting perspective to family magics. Sirius Black is also quite popular. His knowledge of the Black family magic and his rebellious nature make for great storylines. Additionally, Ginny Weasley, with her strong Weasley family ties and her own magical abilities, often features prominently.
Luna Lovegood might be a great character in this fanfiction. Her own family situation is a bit different and she has a very open - minded view of the world. She could be a source of comfort or inspiration for characters dealing with family trouble, and her quirkiness could add a new dimension to the story.