If I remember right, this should do the trick:
Code:
/cast [target=party] Mark of the Wild
just change the spell name to whatever the buff is on each character and bind it all to the same key so when you press it everyone activates the macro. Either that or:
Code:
/target party
/cast Mark of the Wild
One of those 2 should cycle through your party members and use a buff, just dont spam it too fast or you might double buff the same person.