Drouin, Suzuki, and Petry should do it, even with the Flyers pushing for the playoffs.
Couturier is a top shutdown center with back to back 70 point seasons, but he played those entire seasons with Claude GIroux. Before that he didn't break 40. I know Philly wants to keep improving, but Drouin just got 53 points as a 23 year old, without Giroux. Put him on Giroux's line, and Drouin gets seventy points, just like Giroux. Suzuki makes up for the high-draft-pick expectations Couturier still carries, for whatever that's worth. Petry makes up for Couturier's defensive impact, and the addition of Petry to the blue line lets the Flyers swap out an inconsistent, all-offensive defenseman like Ghost for another star forward like Nylander or Laine, so they come out way ahead on offense, even on defense, and add a top prospect in Suzuki. They've got 13M in cap space, so even though Couturier's a great deal, I think they do all of this without having to clear any more space. 8.7 for Couturier and Ghost out, 7M in for Nylander, 5.5 for Drouin, 5.5 for Petry.... yep. They finish with 3M in cap space, and 21 players. Done.
Joke's on Montreal, though, because without Giroux, Couturier might never break forty points again. I think if you need a 35 point shutodwn center, you could probably get Lars Eller back for just, like, Drouin and Suzuki.
{/sarcasm}