As someone who has already boxed 3x DK's in Beta this is what I will tell you.

Multi-melee mulit-boxing is a different animal than caster multi-boxing. You have to posistion your followers in different angles and ways so as to be sure that your followers are in range to hit the main's target due to every class having a 5yd melee swing range.

Every class that is except Tauren who have a 9yd melee swing range. What does this mean exactly? If you have all tauren followers and anything but a tauren for the main, you will simply be able to run right up to a mob with say an Orc Main and your Tauren followers will be in range to swing at the mob with no extra manuevaring needed.

{Mob}{Main}
{Tauren}

Not much of a diagram but just gives you a visual idea of what I'm talking about.


So, anything but a Tauren for a main and all tauren for the followers and you'll bypass the whole melee out of range ordeal (unless of course you're main dies in which case you'll still need to be familiar with how to properly angle your alts to be able to hit the target).

Now you have one other problem with DK's specifically and that is that due to the nature of their resources, Not all of your DK's will have all of their abilities availible at the exact same time which will create the need to spam your DK's abilites which will limit the potenial to deal burst damage the same way you can with casters. In other words due to misses/resists on some of your followers, there will be times that some of your DK's will have more runic power/runes availible to some of your DK's but not others. I had the same problem with my warriors. Right off the bad 2 of the warriors would completely miss. 1 would crit and the last would get a normal hit which would put all 4 of them at very different levels of rage. It isn't a huge problem, but it is something you should be aware of and have a plan to deal with should you choose to MB multi-melee.

So to sum it all up, my advice would be...
-Pick anything but a Tauren to be your main
-Pick all Tauren followers
-Have a plan on macro creation to deal with varying levels or resources availble to each DK


Last thing to note. You're not really going to be soloing any major instances or really be viable in PvP with this group. It's going to be more of a novelty thing tbh.