What poems did milton write in octosyllabic couplet IL Penseroso On his blindness the late massacre piedmont Lycidas?

You're very close! Here's the breakdown of Milton's works and the forms they use:

* "Il Penseroso" and "L'Allegro" are both written in iambic tetrameter, which is 4-beat lines, not octosyllabic couplets (which are 8-beat lines).

* "On His Blindness" and "Lycidas" are NOT written in couplets. "On His Blindness" is a sonnet, and "Lycidas" is a pastoral elegy written in a variety of forms, including blank verse.

* "The Late Massacre in Piedmont" is the one poem that is written in octosyllabic couplets, a form commonly used for narrative poetry at the time.

So, the only poem on your list that is written in octosyllabic couplets is "The Late Massacre in Piedmont".