I've been struggling with this one for a long time and it's really kept me from moving forward. My main character starts off as a queen consort, and the death of her husband and her stepson (co-kings) are supposed to serve as the inciting incident. But I'm struggling with whether to introduce her husband and stepson alive or have news of their deaths brought to my MC. My MC's husband is very important for the context of the whole story, and his past actions have consequences until the very end, and he'll be mentioned frequently throughout, but on the other hand I think it'll be a little jarring for him and his son (her stepson) to be introduced only to be killed in the same chapter. So would it be best to just have them die offscreen? I really can't decide what would be better.
What is 'better' is entirely subjective. You need to consider what your story looks like, and at what powerful point you want to begin telling it. It will affect so much about how it will ultimately come across.
There is little point describing a normal day in their lives and then kill them, because most modern readers (and editors) won't let you get to that point. If, however, you can have them add dramatic value and conflict before they die... then it may be interesting to show that.
Considering the archetype of story you seem to be trying to tell, it is not unusual to have the declaration or discovery of their death be the very first scene in the book. What this does is, for one thing, start the plot immediately while creating a whole barn full of useful questions to the author.
Ultimately, your question cannot be answered. If they are to die in the first chapter regardless, and you fail to decide -- write both versions of that chapter, and feed them to alpha readers. See which they enjoy better, and which creates the questions you need to push your story forwards.
Either way could work well. I have read novels in which a character dies inn the first chapter, even inn the opening scene, and the repercussions of that death are a major driver of the plot. David Weber's Mutineer's Moon is an example that comes to mind. Another is the killing of King Brion in the first chapter of Kurtz's novel Deryni Rising. The protagonist for the rest of the novel is the king's son and heir, Kelson.
Having news of a death start the plot is so common it is almost a cliche, but it also can work very well. Or the news od the death could be delivered at the start, but later we could see the King alive in a flashback scene. Without seeing your full story, there is no way to say what would work for that story, and you as the author must decide what will work for you and your story.