Is it permissible for a husband to ask his wife to return to him while she is caring for her sick mother, out of fear of falling into temptation himself, knowing that her mother has a living father and a married brother who are well-off? And would this cause harm to her mother?

Marriage is a fortress for both spouses, and the husband must summon his wife to return to him, because her mother's illness is not a religiously valid impediment to the husband's request, especially with the availability of communication means that enable the wife to check on her mother and fulfill her duty of filial piety.