After you get them all in there you will have to derate them.
You could put 26 or 27 THHN/THWN in 2" PVC 40 or RMC. With 21 current carrying conductors you have to derate them to 45%. That would give you an ampacity of 33.75 Amps. To get the rated ampacity of 6 AWG with 3 in a raceway, with that many in the raceway, you would need approximately 2 AWG copper (130 Amps at 90 C with 3 in a raceway).
So the real answer is that you shouldn't even consider filling a 2" conduit with 6 AWG.
More than six (6) current carrying conductors of 6 AWG in a raceway runs you into the law of diminishing returns. Nine CCCs may work under certain load conditions.