You're facing an issue due to quasi-connectivity. Working around quasi-connectivity can get fairly difficult sometimes, but it's very useful for many things, too.
A 0-tick pulse does not trigger quasi-connectivity, so a structure like this will only move the diamond block:
Repeaters update before comparators do, so after you push the button the repeater will send a signal through the gold block. Then the comparator powers the sticky piston, which pushes away the gold block, so the redstone signal ends in the same tick as it started.
This triggers the middle piston and neither of the other two pistons, it then imidiately retracts. A sticky piston will not pull a block if it received a very short redstone pulse and it pushed a block due to that pulse.
If you use that knowledge, then you could build something like this:
This can be used for a 2x3 piston door, where the lowest block opens and closes first and the highest block last. The offset can easily be controled with the repeaters on the right side and you can add more repeaters for even more offset.