Activate piston on command?
Solution 1:
/setblock ~ ~-2 ~ redstone_block
Activate it and 2 blocks under the command block will be a redstone block above the redstone block place another command block above the redstone block saying:
/setblock ~ ~-1 ~ air
From the redstone block put redstone to the pistons or better yet
/setblock (x y z of one block under piston) redstone_block