Obviously Naruto and Kushina are the most important. But Minato, Naruto's father, also plays a big role as he is part of the family. Also, characters like Jiraiya, who was Minato's teacher and had an influence on Naruto as well, could be important in the fanfiction.
The key characters would be Naruto and Kushina for sure. Then there's the Fourth Hokage, Minato. He was Kushina's husband and Naruto's father. Additionally, the Uzumaki clan members could be important. Even if they're not directly in the story all the time, their legacy and the family's past are relevant. For example, an older Uzumaki relative who passed on some wisdom to Kushina that she then passes on to Naruto.
Obviously, Naruto and Kushina are must - includes. Minato is also very popular as he is Naruto's father and Kushina's husband. Another character could be Jiraiya, since he was Minato's teacher and had an influence on Naruto's life too.
One possible fanfiction could be about Minato and Kushina watching over Naruto from the afterlife as he grows into a great ninja. They could be his silent guardians, influencing his decisions in subtle ways.
Yes, there are many. Some fanfictions focus on the warm family moments, like Naruto's father Minato being excited and taking care of Kushina during her pregnancy. They might show how the village is also preparing for the arrival of the new baby, with friends and neighbors being supportive.
Minato could be a common character. Since he was Kushina's husband in the original story, his presence might add some interesting dynamics to the harem scenario. Another could be Jiraiya. His connection to Naruto and his reputation as a bit of a ladies' man could make for an interesting addition to the story.
Obviously Naruto is a crucial character as he is the host of the Kyuubi. His family members like his father, Minato, and his mother, Kushina, are also important. Minato was the Fourth Hokage and had a role in sealing the Kyuubi within Naruto. Kushina was the previous Jinchuriki of the Kyuubi.
Obviously, Ino is a very important character. Her father, Yamanaka Inoichi, is also crucial as he has a lot of influence on Ino and their family. Ino's mother, although not as much in the spotlight, can play an important role in family dynamics. And then there are Ino's friends like Sakura who could interact with her family and be part of the story in some way.
Iruka could be one of the characters. He has always been important to Naruto, and he might try to help Naruto or at least be concerned about his exile. Kakashi could also appear. He has a connection to Naruto and might be conflicted about the situation. And then there are Naruto's friends like Sasuke and Sakura. Sasuke might understand Naruto's feeling of being an outcast more than others, and Sakura could be torn between her loyalty to the village and her friendship with Naruto.
Jiraiya could also be one of the main characters. He was Naruto's mentor and had a connection with Kushina's family. He could play a role in helping them adjust to the time travel and also use their knowledge to his advantage in some ways, like getting intel on future threats.
Minato might be a common character. Since he is Kushina's husband in the original story, his presence can add an interesting dynamic. Also, Jiraiya could be there. He was Naruto's mentor and his interactions with the harem situation could be quite humorous.
Imagine a fanfiction where Kushina and Naruto team up to solve a mystery that has been plaguing the Uzumaki clan for generations. They travel to different villages, meet new characters, and in the process, Naruto learns more about his mother and his own identity, which in turn helps him become an even better leader for the Hidden Leaf Village.