All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
No doubt that dutifulness to parents is one of the Sharee'ah and natural obligations on children, especially when their parents become old.
Allah Says (what means): {And your Lord has decreed that you worship none but Him. And that you be dutiful to your parents. If one of them or both of them attain old age in your life, say not to them a word of disrespect, nor shout at them but address them in terms of honor} [Quran 17:23]
Thus, we state that every one has to do his best to satisfy his parents and to please them. Therefore, it is your duty to remove everything that may make them angry and unhappy. Also, be careful of taking their unjust stand as a legal excuse to disobey them; otherwise, you will lose this worldy life and the Hereafter.
Furthermore, you have to avoid returning their injustice in kind or degree. On the contrary, you have to show patience and good treatment even though they show the opposite. It is your duty to be dutiful and Allah will reward you.
In conclusion, these parents are to fear Allah and to help their son to be dutiful. It is their duty to show mercy, kindness, love and gentle treatment. Then, all should know that injustice is a major sin.
For more benefit on the limits of obedience to parents, please refer to Fataawa 271255, 131695, and 123554.
Allah knows best.