Where do you stand in each category? That would be useful to know.
I'd be wary of letting go of Tavares, since by 2018-19 he could be on a new team and poised to be very elite. If you trade him, he becomes someone else's keeper and that could hurt.
My guess is you won't be retaining Atkinson, in which case you probably should explore selling high. Yes - it seems like he's done enough to prove he's the real deal; but nevertheless his value likely will never be higher than it is now. If not him, then Hedman, since he likely won't be a keeper over Burns. Of course you'll lose production by getting rid of them, but in doing so you probably can upgrade at LW and goalie, where I'm guessing you're weaker than average.
Good luck.