What is the ruling on someone who propagated hadiths they thought were authentic, then discovered they were not authentic? Is it sufficient for them to delete them, or are they obligated to inform those to whom they sent them?

Whoever publishes a weak hadith (definition) that should not be published must correct the error by deleting the hadith from videos or by informing those to whom it was sent of its weakness, to the best of their ability. If one is unable to correct the error due to the video's widespread distribution and lack of control over it, then they are not held accountable; as Allah Almighty says: "Allah does not burden a soul beyond its capacity."