Me with friend from guild(me tank +companion dps, him heal + companion heal) did 2 FP. Boarding party, Fundary. And in 3 person Colicoid and Red Reaper. So it is fully possible to do FP with companions.
Well I'm guardian tank, my friend is a Shadow DPS, if we rolled with 2 x healer companions would that prove sufficient? a little challenge isn't a problem and if we need to out level a flashlpoint by a level or 2 we can do that, we just prefer to tackle the challenges with just the 2 of us.