Brian McTaggart has the full list of Astros' players participating in the 2013 Instructional League. Click the link and look for yourself, there are too many to list here.
But what the heck is the Instructional League?
I saw it described as a "baseball boot camp." Jason Parks referred to it in this way:
(It's) a developmental league that starts soon after the minor-league season
ends, mostly for players with immature skill sets who are in need of
specific instruction, refinement, and education. It’s a place where
young players set to continue (or begin) their stateside experience can
learn the ways of the force, a place where their road to the majors
often begins. It’s Professional Baseball 101 for most participants, a
MiLB's Lisa Winston:
Instructional league is usually about teams bringing in their younger,
less experienced players for some intensive training, "bringing up to
speed" and "getting to know you" work. Injured players come and rehab,
players who need to make up for lost time.
Ben Badler (on the Instructional League and international prospects):
Aside from going through the normal baseball work of instructional
league, many teams provide international players with classroom
assignments. Players work on learning both English and what teams refer
to as "Baseball English." They learn computer skills and other basics of
how to conduct themselves as professionals and how their life will be
in a new country.