How can I repent for a sin I may have committed by killing my husband using a spell that led to his death shortly after it was buried, given that I cannot fast or free a slave due to my old age and illness, and how can I repent for my deceased mother who shared with me in this act?

Sincere repentance from the sin of seeking out sorcerers and charlatans requires regretting what has passed, resolving not to return to it, seeking forgiveness, and asking Allah for pardon. Atonement by killing is not necessary because it is not established that magic was the cause of the husband's death, and it is difficult to prove that now. The killer is the sorcerer, and he is the one from whom retribution is sought or from whom blood money is demanded. What is obligatory is sincere repentance and asking Allah for pardon and forgiveness; no expiation or blood money is necessary.