How can one deal with parents who disown their son and hate his wife, despite his repeated attempts to maintain family ties, and their rejection of any religious advice?

Maintaining ties with parents is obligatory in all circumstances, even if they are disbelievers who command disbelief. How much more so, then, with Muslim parents? It is obligatory to honor them and treat them kindly, even if they are harsh, for Paradise lies beneath their feet. As for relatives such as siblings, maintaining ties with them is obligatory, but to a lesser degree than with parents. It is obligatory to maintain ties with them even if they mistreat you, for in the Hadith: "If you are as you say, then you are as if you are feeding them hot ashes, and you will continue to have a supporter from Allah as long as you remain upon that." Maintaining ties of kinship has degrees; the lowest of them is to abandon boycotting and to maintain ties through speech, even if it is just by offering salaam.