What if parents disrespect their children. Some time parents disrespect their own children they abuse their children. We often heared about the rights of parents but what about rights of children of age more than 20 who are still depending on their parents.
"Although the father deserves to be warned (of divine punishment) for his sin and neglect of shar‘i duties, disobedient children and those who do not treat their parents kindly are also warned about their actions; it is not permissible to repay mistreatment with mistreatment or wrongdoing with wrongdoing.
Although children are not to be blamed for feelings of resentment in the heart towards the father who commits sin or is a disbeliever, that does not contradict the duty to treat him kindly and obey him in that which is right and proper. But you have to hold your tongue and refrain from speaking badly to him (father), and also refrain from mistreating him in practical terms. " (https://islamqa.info/en/answers/176847/hating-an-unjust-father)
So from the aforementioned FATWA, one may conclude that children must treat kindly with their parents even if they do injustice with their own children. Children should also follow their parents as long as it does not lead to Shirk.
“But if they (both) strive with you to make you join in worship with Me others that of which you have no knowledge, then obey them not, but behave with them in the world kindly, and follow the path of him who turns to Me in repentance and in obedience. Then to Me will be your return, and I shall tell you what you used to do” [31:15].