I think there is literally no chance they're dealing Castillo unless Baltimore offered up Holliday +, and even then, I don't think Seattle would do it.
Duran makes sense for them to patrol a big park next to Rodriguez. They could put him in LF and he'd probably be a pretty good defensive player there, especially with his arm mitigated in LF. They moved their closer (Seawald) to Arizona last year for their own version of Abreu (Dominic Canzone), but also of course moved Kelenic. They do have both Munoz and Brash in their bullpen, which is a nice place to start, though Munoz did have some struggles down the stretch last season when asked to close full time.
Something like Duran, Jansen and $16m to cover his salary for Woo might work for both teams (assuming Seattle is trying to sign Snell).
Kirby, Castillo, Snell, Giblert, Miller is still an absolutely filthy rotation. Duran helps their offense and defense in LF. Jansen closes for a year and allows Munoz and Brash more time to grow into the role.
Woo would be another version of Crawford, one that I'll call a little bit better since one posted his MLB numbers at age 23 (Woo) and the other at 27 (Crawford), but they're similar in terms of both look like really good bets to be SP4/5 types at worst, both could be more.
@Max Power it's Bowden, so nothing is out of the realm of possibility.