Sam may struggle with getting reliable transportation to get to his money - making opportunities. Since they usually rely on the car, and he's trying to fix Dean's car, he might have to rely on public transportation or hitchhiking which can be unreliable. Also, he may run into people who try to take advantage of him. For example, if he's doing odd jobs, some customers might try to pay him less than what he's worth or make him do extra work without extra pay. This can slow down his progress in getting enough money for the car.
Well, Sam could try getting a part - time job. Maybe he could work at a local diner or a garage. Working at a garage would be quite fitting since it's related to cars. He could earn some extra cash by helping out with car repairs or maintenance.
A possible plot could be that Sam discovers an underground fighting ring where the prize money is huge. He decides to enter, thinking he can handle himself. But he quickly realizes that the fighters there are much tougher than he expected. Meanwhile, Dean has no idea what Sam is up to. Sam endures several tough fights, getting injured in the process. However, his determination to get the money for Dean's car keeps him going. He eventually makes it to the final fight and if he wins, he'll have enough money to fix up Dean's beloved car.
Bobby could be a big help. He might have some old contacts who could offer Sam some odd jobs or even some valuable items to sell. Another person could be Castiel. He could use his angelic powers to help Sam find something valuable that he can turn into money. Maybe he could lead Sam to a hidden treasure or a rare artifact that has a high value.
In fanfiction, they could face the challenge of magical threats. There might be dark wizards who target them because they know a child of Harry and Ginny could be very powerful. This would make them constantly on guard and less relaxed about trying for a baby. Also, they might struggle with their own insecurities. Harry could be worried about passing on his difficult past or the burden of being 'The Boy Who Lived' to his child, and Ginny might be concerned about how motherhood would change her life and her identity as a strong, independent witch.
One challenge could be dealing with other students who don't understand his over - protective attitude towards Harry. Some might think he's being too nosy or interfering. Another might be that he has his own studies and responsibilities at Hogwarts which could sometimes conflict with his protection duties.
One challenge could be finding enough Uzumaki descendants. Since the clan has been through so much, there may be very few left. Another might be dealing with the political implications. Other clans might be jealous or fearful of a resurgent Uzumaki clan.
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.
Another issue could be resistance from other forces. There might be some dark entities or villains who don't want Naruto to control the heartless. They could try to stop him, either by directly attacking him or by using their own powers to counteract his control methods.
Well, he might start by showing Ginny how much he has changed. For example, if he used to be a bit jealous, he could show her that he's now more confident in himself and in their relationship. Another strategy could be to remind Ginny of the good times they had together. He could bring up a special memory like their first date or a trip they took. He might also try to befriend Ginny's friends and family again to get in their good graces and have them on his side.
There can be many challenges. Maybe the big brother has to deal with external threats or has to balance his own life while protecting.