Does the father still bear the sin of cutting off family ties after attempting reconciliation and the grandfather's refusal?

It appears that the grandfather made reconciling with his father conditional on mending his relationship with his sister. The father advised us that he should return to his sister with kindness and maintaining ties, because she is from the kinfolk whom Allah has obligated to be joined and forbidden to be severed, and He cursed those who sever them in His saying, the Almighty: "Then would you, if you turned away, cause corruption on earth and sever your [ties of] kinship? Those are the ones whom Allah has cursed, so He made them deaf and blinded their vision." Therefore, he must take the initiative to maintain ties with her even if she wrongs him, for "the one who maintains ties is not the one who reciprocates, but the one who maintains ties is he who, when his kinship is severed, joins it." If he takes the initiative to mend his relationship with his sister and his father insists on severing ties with him, then there is no sin upon the father at that time, provided that he does not fall short in what he is able to do concerning his obligatory kindness to his father, and he must utilize any opportunity to mend his relationship with his father while frequently supplicating for him.