Sorry, I play on 5 computers, so not much help on same computer issues.
For geting everyone in range. I have my alts follow my main. So it looks like: (this is going to look ugly)
" X
#$%&"
All the alts are on top of each other and about 2-5 yards behind my main. I use LB(on shammies), throw (on my warrior for mixed group), or rank 1 arcane shot( on my hunters) to pull mobs with my alts only. So the mobs all walk up and stand pretty much on top of my main. So everyone is able to melee with no problems. If the mobs move, I just use the /follow key/macro to move my alts using my main to steer them (usually walk through mob about .5-1 yard on other side). Haven't had any problems so far. For my mixed group, I usually have my warrior charge so he is out in front alone since everyone else is ranged. I know that last part doesn't help, just mentioning it.

So my suggestion is to just range pull with your alt, and then the mob should be in range for all to melee. Good luck. Hope that helps.