Is the fiancé entitled to inform his mother of his fiancée’s non-chronic illness? Is she entitled to request a divorce because of it? And is he obligated to fulfill her request, knowing that she will object and has already taunted the wife of her other son due to her illness?

There is no sin upon the husband in informing his mother of his wife's illness, nor is he obligated to do so. And if she advises him to divorce her, he is not obligated to comply with her. The husband should try to reach an understanding with his wife so that he does not inform his mother of her illness, to avoid her objection and her striving to have her divorced, unless the husband desires divorce and uses his mother's satisfaction as an excuse. Divorce before consummation and having children is better than divorce after them if the spouses know that their marital life will not be sound.