Is it permissible to write a will that includes religious matters such as not wailing, not holding a condolence gathering, not wearing black, and women not following the funeral procession, and specifying who washes the deceased, even if the testator does not own any money? And who is the appropriate person to be seriously informed of this will?

It is permissible to write a will concerning all that has been mentioned. Fatimah and Aisha both willed that their husbands wash them [after their death]. Ibn Al-Qayyim mentioned that some of the Salaf willed that Surat Al-Baqarah be recited at their graves. The testator must enjoin his family not to commit religious transgressions, such as wailing, and should not pay attention to anyone's mockery, for this is his duty towards them.