The Pistons took Mitchell and Siva in the second round of this year's draft.
Mitchell has appeared in 10 games with the Pistons, averaging 1.1 points and 1.1 rebounds per game. He was drafted 37th overall out of North Texas.
Siva has appeared in 13 games with the Pistons, averaging 5.8 minutes. Siva, the 56th selection in the draft, won an NCAA championship as a senior at Louisville.
The Pistons announced the moves on Thursday.