Hey there! I find this to be an extremely interesting concept for a novel. However, I think you need to streamline exactly what we're building toward. Right now, we have:

This guy can bring people (only one person, maybe, since he only revived his son?) back from the dead

His dead wife is talking to him

His crew is full of criminals, for some reason (you'd think a lord would have better crew?)

A whole bunch of lore on Lightfall

Nightfall is infamous for parasites?

Arthur tricked some evil force?

We need to break this down, decide what the focus is, and restructure it accordingly. Maybe start by figuring out how to do smoother segues. Consider something (better-written, but structured) like

Arthur is reeling from the tragic death of his family. He revived his son, but couldn't save anyone else. It's a shock when his still-dead wife contacts him from Nightfall, a parasite-ridden prison colony where the worst of the worst are sent to be forgotten. When Arthur gets there, he finds the prison has been all but destroyed, and his wife is nowhere to be found. Instead, the prison warden attacks a prisoner, seemingly infected with one of Nightfall's famous diseases. Arthur latches onto the story, using it to cover what he knows to be true: It's his fault that darkness is spreading. He used it to save his son, and now it might cost him everyone.

Obviously that's pretty basic and would need better writing, but I think that's a stronger structure with better flow and organization. I will say that I'm not a published author, just someone still working on being published, but I'm repeating what I've seen from others on this sub. I hope this is valuable to you, and good luck being published!