Is accusing the deceased of sodomy considered a slander (qadhf), like accusing chaste women? What is the ruling on hastening in that then rectifying it? And is being absolutely certain of the act without the presence of four witnesses considered slander?

Slander (Qadhf) includes accusing both males and females of indecency without evidence. If you attribute the act of sodomy to a young man based on what you heard, this is forbidden slander, even if you follow it up by saying, "According to what I was told." However, if you were informed that some people are saying he was killed due to sodomy, this is a نقل (transmission) of what some people are saying and not slander. Nevertheless, it is impermissible due to the harm it inflicts upon the deceased and their family. The duty was to conceal it and not spread it.

Committing the indecency of adultery or sodomy is only proven by four eyewitnesses who saw it directly. The obligation is to refrain from speaking about the dead.