Outfield is certainly one of the places that the Orioles need to make a decision (or 2).
Hays (LF), Mullins (CF) and Santander (RF) is certainly a reasonable option, the first two with 2 years of arbitration remaining and Santander in his final season of club control arbitration.
Cowser struggled in his debut but has produced well at AAA and Kerstad looked ready with decent ML debut and big AA/AAA numbers.
McKenna is signed (ARB1) and is a good 4th OF. Orioles added Hilliard who they also signed to a ML contract and doesn't have any options.
Haskin didn't get protected on the 40 and Stowers is stuck at AAA.
Everyone can't play.
Santander seems like the obvious trade given his ARB3 salary (12-13M) and the simplicity of replacing him with Kjerstad or Cowser.
I'd guess Hays and Mullins are tied together a little bit in that you can extend both or neither.