Hey, been lurking around this forum for ages, got a team of four level 80 shammies myself, and I thought I'd give you a hand.
First of all, what you are doing is leveling your friends char for him, which is classified as accountsharing. And as we all know, accountsharing is bannable.I'd advise you to just ask your friend when he's got some spare time so you can level together. If you somehow go through with this (don't!), you'd have to make a macro on each one of them:
Priest macro:
/cast [target=DRUIDNAME] Renew
Druid macro:
/cast [target=PRIESTNAME] Rejuvenation
But I'd strongly advise not to play on a account that not has your own name under it.
You could just try and get your own second account(maybe a trial one just for fun!)

Regards

Inekthera