What is the legal ruling on marrying a widow who desires it for fear of temptation, while her family and children oppose it?

There is no objection to the woman's guardians discussing with her, and encouraging her to stay with her children and raise them, and to forgo marriage if she can manage without it.

However, if she fears falling into the forbidden, it is not permissible for her to abandon marriage; because protecting oneself from sin is paramount, and the soundness of one's religion is above all else.

In this case, neither her children nor her family have the right to prevent her from marrying a suitable partner. If her guardian prevents her, he is deemed to be unjustly obstructing her marriage (عاضلاً), and it becomes permissible for her to be married through another guardian, or to refer the matter to a judge to marry her off.

This should be clarified to her children and family, and they should be warned of the consequences of oppressing her.