Ernest Jones and Jared Reed are free agents. Riq Woolen, Kenny McIntash, Mafe, Abe Lucas, Geno Smith and DK can be signed before they reach free agency next year. Seattle has the 3rd worst salary cap space in the NFL. I hope you are correct.
Our salary cap space is bad, but not nearly as bad as people think.
The thing we have going for us is... we have basically no dead money on the books for next year. All the money we 'owe' is to players we can restructure, extend, or cut.
As smellyman pointed out, we have 3 guys we are almost certainly releasing (G. Fant, D. Jones, and PROBABLY Lockett

) and we are already out of our cap hell. Add on extending (or trading) Geno and DK, and we'd have plenty of space for both Jones IV and Garrett, and that's before we get into figuring out tougher calls like Noah Fant and Uchenna Nwosu.
We have work to do regarding our cap space situation, but most of it is in-house accounting stuff, not super tough personnel decisions. (If we bring on Garrett, we aren't re-signing Jarran Reed, so that's a contract we don't need to worry about).
The real issue is if we are choosing to make a big splash move at DE, we probably can't afford a big splash move at IOL.