This.
Sound 5 could win if the OP means Kankuro and Temari by "Sand Siblings" though. Kimimaro could probably solo one of them (Kankuro or Temari) high diff.
Unless Kimi if very Careful and Doesn't Underrate them he can Be Killed.
Temari's Wind Jutsu could Slice him Or his Bones if he isn't Careful, Wind Jutsu's excell are Cutting Through Stuff, Take Danzo Splitting Susanoo for example Or Temari Cutting Down a Large Area of Forest in part one with just One Jutsu
kankuro's Poisons will Affect him if he Allows himself to get Scratched Befor he can defend himself with his Bones.
Kimmimaro takes gaara(keep in mind he, would have to fight two enemies before gaara so even if he sick he still wins )
kidomaru & tayuya > kankuro
Fat boy & twins > temari
I'll go for sand siblings. Even if it's in the first phase, they're pretty powerful. I mean the sound were defeated by the Konoha 11 who at that time were not so powerful as today, why the sand couldn't do that, since they're stronger than the others at that time?