Illicit Relationship and Forged Document

My brother married in 2015 to a woman who had been previously married and had a son from her first marriage. Initially, my family did not support their marriage because my brother and sister-in-law had an extramarital affair. Despite our concerns, my brother was determined to marry her. Problems arose soon after, as my sister-in-law was very lazy and resisted having another child even when she became pregnant. During her pregnancy, she refused to eat properly or take any medication, causing complications. In her seventh month, doctors warned that her behavior could severely impact the baby's health, potentially leading to a physical disability. Fortunately, my parents intervened during the last two months of her pregnancy, and she eventually gave birth to a healthy baby. However, my brother and sister-in-law's relationship remained strained due to the difficult pregnancy. Their son has primarily been raised by our parents, as my sister-in-law has shown little interest in caring for him, focusing instead on her elder son. In 2019, my brother got a job in another city and helped his wife secure a job at a residential school. Due to unforeseen circumstances, he couldn't go, but she moved with her elder son. In 2020, the pandemic caused my brother to lose his job, leading him to start a business that didn't succeed. By 2022, he began urging his wife to find a job nearby so they could live together again, considering our aging parents and the younger son's desire to be with his parents and elder brother. However, she seemed unwilling to reunite the family. Later, the elder son revealed that his mother was having an affair, providing evidence such as text messages and calls. He hoped to end the affair by bringing the family together. My brother tried discussing the issue with his wife and her parents, but they refused to address the problem and pressured the elder son to stay silent. Despite my brother's efforts, the relationship remained distant, with his wife visiting only during holidays. In June 2024, my brother discovered more incriminating evidence of the affair. When he confronted her parents again, they blamed him of fabricating the situation. His wife reacted dramatically, accusing him of violence. Given the circumstances, my brother now wants a divorce. However, my sister-in-law refuses to agree to a divorce for four years until her elder son completes his 12th grade. This is not out of concern for his education but because she has illegally changed his surname to ours. My brother knew about the new surname but couldn't challenge her due to her dramatic reactions. We are concerned about the legality of changing the elder son's surname without proper consent, which could negatively affect his future. Additionally, we want to address her affair, especially since it involves a colleague at the school where she works, who is married with children. We are seeking advice on obtaining a divorce and correcting the elder son's doc