Sorry to say this, but /castsequence only works with a single target assignment.

Code:
/castsequence [target=focustargettarget,exists] Power Word: Shield, Renew
/castsequence [target=focus, exists] Power Word: Shield, Renew 
/castsequence [target=focustargettarget,exists] , Renew
/castsequence [target=focus, exists] , Renew

Might work. I'm currently waiting in an hour long queue so I can't test it. As long as each conditional is specific enough that only 1 spell can evaluate and fire then the macro should work.