stage 2 would be freakin impossible. first of all, you need to keep all 16 debuff slots full, or else she will deep breath multiple times..
deep breath is avoidable, yes, but there are also a shitload of whelps in stage 2 which can cause major problems for only 10 people
stage 3 is also hard, especially for healers, when you are constantly getting feared and hit by lava.
finally, the DPS of only 10 people on Onyxia, with only 4 healers, would take FOREVER. something is bound to go wrong, executed perfectly i still don't see how it would be possible.
idk maybe it is possible, i could just be stupid