Is it forbidden for the children and brothers of a sixty-year-old woman to refuse her marriage, and is it permissible for the questioner to be her guardian after they refuse that?

A woman's son has a greater right to give her in marriage than her brothers and her nephew. If he refuses to marry her to a suitable suitor, then he is preventing her from marrying. If the closest guardian refuses, then the guardianship transfers to the next closest or to the judge. If her brothers also refuse, then you may marry her, but it is preferable to refer the matter to the Sharia court to avoid disputes. Old age is not an impediment to marriage.