Is it permissible to designate money for investment and make its returns an ongoing charity (Sadaqah Jariyah) on behalf of oneself, the living, and the deceased, on the condition that the principal amount is not disposed of, and only the returns are used for needs? Does this require the consent of the heirs currently? And is a will to that effect valid after death if the project was not implemented during one's lifetime?

It is permissible to invest money and designate its proceeds as an ongoing charity (Sadaqah (definition) Jariyah) on your behalf and on behalf of whomever you wish, and this is one of the best acts of drawing closer to Allah. You can make it an endowment (Waqf) during your lifetime by tying up the principal of the money and making its proceeds charity; in this case, the heirs cannot revoke it after your death. However, if you condition the endowment upon your death, it takes the ruling of a bequest (Wasiyah) and is executed only within the limits of one-third of the estate. It is permissible to include needy relatives among the beneficiaries of the endowment. It is advisable to consult with scholars to determine what is most religiously optimal.