Definitely Bran Stark. His powers as the Three - Eyed Raven open up so many possibilities in fanfiction. He can time - travel, see the past and future, and this can be used in all kinds of creative ways to help the Starks. Then there's Robb Stark. His military leadership and the 'King in the North' aspect can be further developed. We can see more of his strategic thinking and how he could have changed the fate of the Starks had he not been betrayed. And let's not forget Rickon. In some fanfictions, he's given a more prominent role as a wild and fearless Stark, which is really cool.
Ned Stark's honorable nature would make him react with disappointment at the many acts of treachery and deceit in the show. He would likely bemoan the lack of honor among some of the characters. Arya, with her vengeful streak, might cheer on the characters who are getting revenge on their enemies. Sansa, having been through so much, would probably be more empathetic towards the female characters who are also suffering in the story.
Well, perhaps he uses his magic skills. He could cast protective spells around the Starks' territory, like a powerful Fidelius Charm to keep their location secret from their enemies.
There could be characters from Tony's past as well. For example, Obadiah Stane might be mentioned or even be a part of some backstory. If the fanfiction delves into the family history, there could be appearances of their parents in flashbacks. And don't forget Rhodey. He could be a great influence on the baby sister, teaching her about military values or just being a cool older friend.
It could be the White Walkers if this is a crossover fanfic set in the Game of Thrones universe. They are a huge threat to the Starks in their own world, and Harry Potter would have to find a way to stop them.
A new supervillain who has emerged and wants to make a name for themselves. They think that kidnapping Tony Stark's daughter will draw him out and give them the chance to prove they are a force to be reckoned with. They might also be after Tony's wealth and resources which they can access through his daughter.
I'm not sure specifically who Jon Franklin is without more context. He could be an ordinary person with a passion for sharing true stories, or perhaps a professional storyteller, journalist, or writer.
It could be some of Tony's business rivals. They might see the daughter as a way to get to Tony, either to steal his technology secrets or to blackmail him. They could try to kidnap her or manipulate her into betraying her father.
There could be a wise old wizard who gives Jon advice on how to hatch and take care of the dragon. Maybe there's also a rival of Jon's who is jealous of his discovery and tries to steal the dragon egg.
Starks was one of the main characters in Minecraft. He was exiled to a deserted island after being robbed of his manor life in the game, but he managed to defeat the monsters and finally escaped. Starks became a mining expert and found the whereabouts of the criminals, allowing them to receive the punishment they deserved. In the end, Starks returned home, but he was dissatisfied with his dull life and longed to explore the unknown world. The story about Starks could be exempted from reading in Minecraft: Far Voyage.