Help with a healing macro

Is it possible to cast on different targets in a castsequence??

For example, can my priest cast renew on every member of the party?

/castsequence [target=party1] renew, [target=party2] renew, etc, etc

Anyway to do something like the above?

Not in a single sequence. You can use /targetparty /cast renew, which will cycle to a different party member every time you press it, but there's no guarantee that you'll get a "valid" party member every time. Spam it too much, you could cycle targetting through the whole party before renew's GCD is done and end up repeatedly casting on someone who already has renew. /targetparty also excludes player, so it will never cast on your priest.

You can do it with a macro like this:

/castsequence [@player] reset=2 Renew, NULL
/castsequence [@party1] reset=2 Renew,Renew, NULL
/castsequence [@party2] reset=2 Renew,Renew,Renew, NULL
/castsequence [@party3] reset=2 Renew,Renew,Renew,Renew, NULL
/castsequence [@party4] reset=2 Renew,Renew,Renew,Renew,Renew, NULL

Spam it, wait for couple of seconds to reset, repeat, profit?
You need a macro extender for this macro.

Reason why Renew is repeated so many times is that all castsequences which have the same spell as next step will advance forward when triggered. (Make sense?)

I would strongly recommend adapting to healing style where you only heal when necessary. Your mana won't last if you spam heal at 85.