Well,Oda is setting up Luffy to accomplish what Roger and Xebec couldn't,so i think at least Zoro and Sanji should be able to defeat an admiral by EOS!Other straw hats,grand fleet members and allies such as Revs will take care of vice admirals,ssg,cp0,gorosei and IM!
Luffy vs Sakazuki!
Zoro vs Fujitora
Sanji vs Kizaru!
Jinbe and/or Yamato vs Green Bull!
CP0 vs REVS!
Dragon vs IMU!