I have mine set up as just /cast [target=target-party1] <spell whatever> I mean that's really all you need, if you are changing focus between your toons then you should probably set up a macro on said key to also change your party1(Leader) and bam problem solved. And even then you can target with your main dead and still effectively DPS well at least for standing fights anything else you would need to do a quick focus/leader change and move your toons and continue the fight.