It is permissible for the relative to ask for the inheritance even if that is done through the courts
Question

                My mother died and she did not take her legitimate shar’i right from her brother, because she was afraid of severing ties of kinship, but she wanted it. Do we, her sons, have the right to ask our maternal uncle for our mother’s rights even if that leads to severing the ties of kinship between us and him, or the matter ends up going to court?.
Praise be to Allah.
    You have the right to ask for your mother's right of inheritance, even if it means going to court, unless your mother allowed that. If your mother gave up her right to her brother, then you do not have the right to do that. The right is hers. But if she did not give it up, but she refrained from asking and disputing, then you have the right to ask and dispute for your rights, and there is nothing wrong with that. Praise be to Allaah. End quote.