Is it permissible to lend evening dresses that the wife used to wear at unmixed weddings to her relatives for them to wear at mixed weddings? And is it permissible to sell them to clothing stores?

It is not permissible to lend wedding dresses to someone known to use them in a forbidden manner, such as in mixed gatherings. As for selling them to rental shops or individuals, it depends on the prevailing situation in the country. If the norm in weddings is the absence of mixing, then selling them is permissible. Otherwise, it is not permissible to sell them, as a means of blocking the path to corruption and acting upon the Almighty's saying: "And cooperate in righteousness and piety, but do not cooperate in sin and aggression."