One challenge Naruto might face is Gaara's past traumas. Gaara has been through a lot of pain and isolation, which has made him distrustful. It would be difficult for Naruto to break through those barriers and get Gaara to open up. Another challenge could be the political situation. Suna and Konoha have had their differences in the past, and some in Suna might not be happy with Naruto's influence on Gaara. Naruto would have to deal with any potential political unrest or opposition from those who don't trust Konoha.
In a Naruto - raises - Gaara fanfiction, Naruto may struggle with Gaara's jinchuriki powers. Gaara has the power of Shukaku, and if something were to go wrong with that power, it could be dangerous. Naruto would need to find ways to help Gaara control it, especially in situations where Gaara might be pushed to his limits. Also, Gaara has his own way of thinking and doing things. Naruto, with his more optimistic and outgoing nature, would have to learn to respect Gaara's individuality while still trying to guide him in the right direction. This balance could be quite a challenge.
One challenge could be Naruto's impulsive nature. He often rushes into things without thinking, and Tsunade would have to find a way to rein him in. Another might be dealing with Naruto's fame. Since he is the Jinchuriki of the Nine - Tails, he has a lot of attention on him, and Tsunade would need to protect him from those who might want to use or harm him.
Financial difficulties could also be a problem. Naruto might not be well - off initially, and raising a child requires money for things like food, clothes, and education. He would have to find ways to provide for his sister while still being a ninja. Also, there could be threats from Naruto's enemies who might try to target his sister to get to him.
One challenge could be the public perception. The wizarding world may not be very accepting of Hermione raising Voldemort's daughter. There could be a lot of fear and suspicion. Another challenge is Delphini's own nature. Since she has Voldemort's blood, she might have some inborn dark tendencies that Hermione has to constantly fight against. Also, Hermione would have to deal with the memories and legacy of Voldemort that might be a part of Delphini's upbringing.
One challenge could be dealing with their different personalities. Each sibling might have their own desires and goals. For instance, one might be more interested in military matters while another in the arts. Rhaenyra would have to find a way to nurture all of them individually.
In the fanfiction, Kakashi might face the challenge of Naruto's insecurities. Naruto has always had a complex about being alone and not having a family. Kakashi would have to find ways to make Naruto feel secure and loved. Also, dealing with Naruto's powerful and sometimes uncontrollable chakra could be a problem. Kakashi would need to train Naruto to master his chakra properly without it overwhelming him.
Naruto would likely struggle with Hinata's shyness. He is a very outgoing person, and suddenly being in a body that is naturally more reserved could be difficult. For instance, when interacting with other characters, he might accidentally come across as too forward or too quiet, which could lead to misunderstandings. Also, Naruto would have to deal with Hinata's personal relationships. Her friends and family know her in a certain way, and any changes in behavior due to Naruto's possession could cause concern or confusion among them.
One challenge could be cultural differences. Konoha and Suna have different traditions and ways of life. For example, the Hyuga clan has its own strict family rules which might conflict with Suna's more laid - back approach in some aspects. Another challenge is the distance between their villages. Maintaining a relationship while being so far apart for official duties can be tough. Also, their friends and families may have different expectations. Hinata's family might be worried about her moving to Suna, and Gaara's council in Suna may have concerns about a Konoha - native being so close to the Kazekage.
One major challenge would be understanding the magical world. Tony Stark is a man of science, and magic operates on very different principles. He'd have to learn about spells, potions, and magical creatures. Another challenge could be dealing with the wizarding community. They have their own traditions and laws, and Stark might find it difficult to fit in or make sure Harry follows all the rules. Also, protecting Harry from magical threats might be tough for Stark as his technology might not always work against magic.
Their different upbringings might also pose a problem. Sakura grew up in a more normal ninja family environment in Konoha, while Gaara had a very traumatic and isolated childhood in Suna. This could lead to differences in how they view relationships and family. For example, Gaara might be more hesitant to open up fully because of his past experiences.
He might face powerful enemies. For example, if the enemies are from a secret organization with strong and unknown jutsu, Naruto would have to quickly figure out their weaknesses. This could be difficult as he has no prior knowledge of them.