If I use Palossand's "Dust Storm" attack against a Stage 2 Pokemon, do I discard the Basic and Stage 1 cards attached to the Stage 2 Pokemon?
No. The Basic and Stage 1 as well as the Sandygast are part of their respective Pokemon and are not discarded.
Source: Burning Shadows FAQ (2017-07-20), TPCi Rules Team (2017-08-03)

Relevant cards

Note: All applicable cards may not be listed below.
SM3_62