Well, you could try and divvy up the team. 5 is very noticeable and lots of people despise multiboxing. So the more obvious it is, the angrier they get. LFR is mob rule which is important to keep in mind.

Whenever I dual box I get no rage anywhere. Nobody notices because it's natural and appears to be two people playing. So my advice would be take one melee and one ranged at a time. Two ranged isn't bad. That basically means running LFR three times.

A little story: Back in MOP my war + shm + bm * 3 crew sat at the top of the healing and DPS meters for the first leg of SoO LFR. Up to pride. This pissed a lot off. They complained in raid chat and even though some in the raid told them to zip it they kept going. So the raid vote kicked to shut these people up. Even though we were winning half my team got vote kicked. I think that was the last time I ran LFR on more than two characters.