Is the questioner considered sinful or unjust toward his father in the current situation, and will he be repaid in kind by his son in the future, and is his brother's statement true, and must he abandon his expatriate life to return for the sake of honoring his father?

The right of a father is great, for Allah has coupled His gratitude with gratitude towards him, and disobeying one's parents is among the major sins whose punishment is hastened in this world. You should show your father love and compassion, preventing him from overexerting himself, and provide for his financial needs, even if indirectly, knowing that he has a right to your wealth. You should also make him aware of your concern for his religious uprightness. As for returning to live with your father, it is not obligatory, especially if it would harm your livelihood.