I'm not sure for Kollektiv, but I know that Cdew uses the default Blizzard target party 1, target party 2 binds. (F1 for self, F2 for party 2, F3 for party 3). That is changed in the keybindings menu. Means you can press F2, then cast your heal etc.
A macro you could use though, if you wanted separate heals for each party member (seems pointless though), could be:
and this can be shortened to:
/cast [@party1] Riptide
Obviously just changing party1 for party2 in the second macro.