Manually alt-tab to the alt and turn in/take quest as normal; not so bad for 2-3 boxers but a nightmare for 5boxers ;p

I personally play 'em all together from the start so their lvls stay relatively together, though some suggest playing to 10ish solo then grouping. I'd go apeshit insane if I tried to lvl multiple chars in a row to 10 doing the same things that close together instead of all at once though lol

I also prefer questing, and as a dual-boxer you shouldn't have any trouble with most quests; depends on how patient you are, grinding can be a little faster but comes with fewer gear upgrades and no rep gains(my boomkins and even my shamen in my sig were Exalted with SW by 50, meaning cheaper riding/epic riding training now that all rep levels affect buying price)

Greetings welcome, don't feed the Wilburs, beware XZin's links in IRC, and enjoy your stay :P