i tried 3 box rogues and was successful.

your main will lead of course with 2 lagging behind. Once you hit the mob then over shoot him and turn back towards him with your alts following closely behind. Then you work the mob between your 3 toons. easy peesy. The mob will alternate between the two groups and you can constantly backstab or whatever else your rogues are good at. Usually the melee will finish the mob off fast. Your going to have to learn to target fast though. Using the number 1 key(attack) will automatically retarget if u lose it.

3 rogues are a great combination IMO. good luck with them.