It kind of sounds like you have a group of characters that you want to remove their plot armor. If the reader realizes that anyone can die, then they will be unsure who could be next, as any of the main characters could go.
Many people have named George RR Martin as someone who overdoes deaths, however it is unarguable that no one in the A Song Of Ice And Fire universe has any plot armor whatsoever, as central characters can drop at anytime. However, it can be noted that a lot of the characters appear to be dead, but end up returning to the story, meaning that death now is not even final. The mantle of permanent death has been removed, so that characters can potentially return.
A franchise that has overused this is the Marvel Cinematic Universe. So many main characters have come back from feigned death or the brink of death that it's now difficult to believe that even if a character does die, they won't just return at some point, robbing all of the deaths of their emotional impact.
So the trick is to balance between maintaining the emotional impact of deaths that do occur, against ensuring that the characters who will actually make it to the end are not necessarily guaranteed to make it in the reader's mind. It is definitely a tightrope walk.
I think in order to subvert expectations, you need to not allow any expectations. If there is a Chosen One who needs to make it to the end of the story along with a group of allies, then everyone knows that whilst any of the friends can die, the Chosen One can't. So making sure your group is all equal in their goal and their importance to it would be a good way to start.
This is similar to if the POV character stays the same throughout the story; they cannot die because the story will end. It seems like you're doing the POV of a number of characters though, so that should help for the reader to be unaware who can and cannot be killed within the story.
Also, readers will know that as soon as someone pulls out a picture of their family, they are doomed. So if you want to establish the backstory and unique role for a character who is going to die in order to make their death more meaningful (instead of them just being disposable) then you will need to have all of the characters get an established backstory and unique role. This means no one stands out as being the fatefully tragic character, as they all have things to lose, so have the whole group pass around pictures of their own families.
Finally, make sure not to set people up for death. It needs to be believable that all of your characters can make it to the end, even if by the end few of them do. Readers will not want to emotionally invest in any character if they think there is only a 20% chance that they will live. Everyone needs to reach the end for their own reasons, the tragedy comes from when they really should have survived but didn't.