Whose body did Orochimaru sacrifice to summon Hashirama and Tobirama?
During the Chunin Exams, whose body did Orochimaru sacrifice to use the reanimation jutsu?
It was Zaku and Kin from Team Dosu who had both been removed from the Exams following their defeats during the Elimination Round in the Tower of Death (Zaku having had his arms torn up after Shino blocked his palm wind holes. Kin after being knocked out from her head hitting the wall thanks to Shikamaru's Shadow Possession)
No longer inhabited, the First and Second's bodies dissolve, revealing themselves to in actuality be the bodies of Zaku Abumi and Kin Tsuchi, two Genin Orochimaru had entered into the Chunin Exams and had now sacrificed for his means.
Source: Konoha Crush (Arc) > The Third Hokage vs. Orochimaru (6th Paragraph)
on Zaku's and Kin's wikia pages you can see that they were shown after the Hokage's bodies dissolved