Well here is the general concept

If you have one class and you want them all doing the same thing then you have one setup. All the keys can do the same things so it happens across the board.

If you add in another class then you have to have two sets of keys now, one for the first class type (usually a tank) and then another set for the second type of class (Usually DPS). You will first need to do a little investigating to see how much you can combine these keys of 'when the tank does this the dps do that' sort of deal.

It keeps growing from there. In the end its just having to write compatibly timed macros across your characters for the five man set up and then work out how to run two of them at once.

Simple answer: Is it going to be harder than a group of just 1 or 2 classes, YES. But so is just a 5 man group of 5 different classes.