Is it permissible for the parents of the spouses to keep a key to the couple's apartment and enter it whenever they wish?

It is permissible for the parents of both spouses to have a key to the husband's apartment, allowing them to enter it in the absence of the spouses, provided the husband gives permission. Otherwise, no one has the right to enter his home. However, if one or both spouses are in the apartment, entry is not permissible except after seeking permission. If the person entering is a mahram (a close relative with whom marriage is forbidden) and lives with the homeowner, they are not obligated to seek explicit permission, but they should inform the homeowner of their entry. If they do not live there and the door is closed, they should not enter except with permission.