The Kumo ninja would likely be angry at first. They'd feel that Naruto, as a symbol of hope in the shinobi world, should have noticed their problems. But some of them might also be hopeful that Naruto's arrival would finally change things for the better. As for Naruto himself, he'd probably be shocked to realize how much he'd overlooked Kumo and would feel a sense of guilt.
Kurama might become angry at first. He's a powerful being and being neglected would likely wound his pride. He could start causing some minor disruptions inside Naruto, like making it harder for Naruto to access his chakra.
The Z - fighters like Krillin and Yamcha would be curious about Naruto. Krillin might try to befriend him quickly, while Yamcha might be a bit jealous if Naruto starts getting a lot of attention. In the Naruto world, characters like Sakura and Sasuke might not even notice Naruto's disappearance at first if he has been neglected. But later, they might realize the importance of Naruto when things start to go wrong in their world without him. And in the Dragon Ball universe, Piccolo would be very watchful of Naruto, trying to figure out his motives and if he poses any threat to the safety of the planet.
He might become withdrawn. Naruto, who was always so full of life and energy, could start to keep to himself more. He might stop seeking his family's approval and focus on his own path, whether it's through training or making new friends outside of the family.
They could become resentful. They might start to avoid Naruto altogether and refuse any summons. They could also start to act out in the forest, scaring away other animals or causing minor disruptions just to show their displeasure.
She might feel guilty. Since they are siblings, she could be aware of Naruto's neglect and try to make it up to him in small ways, like sharing her food or secretly leaving him little gifts.
Harry might initially feel sad and confused. He could start to withdraw into himself, spending more time alone. Maybe he'll question what he did wrong to be treated this way.
If the grandfather is very warm and accepting, Shikaneji would feel relieved and happy. They might open up more about their relationship and their dreams. Nejire could start chatting excitedly about their future together, and Shinsou would relax and join in the conversation more. However, if the grandfather is not so friendly, they would be disappointed and perhaps a bit defensive.
Perhaps he's been influenced by someone who gives him bad advice. For example, if someone tells him that natural talent is enough and training is overrated. Also, he could be dealing with some personal problems, like a conflict within his family or among his friends that takes up all his time and mental energy, causing him to neglect training.