Is a son considered sinful if he has exhausted all attempts to mend his strained relationship with his mother after his marriage and has not succeeded, especially with the change in family circumstances, the father’s involvement in managing the household, and the mother’s desire for the son to enter into conflict with his father?

The rights of parents are great, and being dutiful to them and obeying them in what is good are among the most obligatory duties. The right of the mother is more emphasized, and the injunction regarding her is greater. You must be dutiful to them, treat them kindly, and obey them in what is good. It is not permissible to abuse them or sever ties. If your mother commands you to do something that does not involve disobedience to Allah, and she has a valid purpose in it, and it does not cause you harm; then it is obligatory for you to obey her in it, even if you find difficulty in it, as Ibn Taymiyyah mentioned. You must maintain ties with her and show affection towards her in whatever way you can and that does not harm you; for filial piety includes conveying all possible good and warding off all possible evil. If you do what you are able to do towards your mother, then her change of attitude towards you or her anger with you will not harm you thereafter, as long as it is without just cause.