If you are doing normal you only need 4 people handling the debuff. 2 tanks + 2 healers makes it easy if you are having DPS issues. On Heroic you need your entire raid doing it. 15-20 stacks should be the goal per debuff.
As for your question on how to avoid having one tank not passing it to the other while soaking cleave it is actually quite simple. Just have the tank without the debuff hugging the boss and the one with the pheromones behind him dropping the pheromone trail.
On normal, I think we used 2 tanks and 2 heals; probably swapped around 20.
On heroic, we use all 9 non-melee DPS; swap at 14.
The tank with pheromones does not DPS (except ranged stuff) and stands around the back range of the cleave. Tanks get almost no vengeance on this fight on normal and same on heroic until p2, so you lose very little DPS by having them kite. If you position absolutely perfectly, you might be able to have both in melee range, but it's not really worth it.
We never cheesed it by having DPS take cleaves, but if you do, I would consider having your healers and your 2 most mobile ranged DPS kite. Swaps are easier this way too.
On normal we had 3 ranged + 1 healer kite it. On Heroic we use healer>tank>tank and then dps etc.
About kiting while tanking. It can be a bit messy, when you have to turn the boss while soaking the Furious Swipe at the same time but it just requires a bit of practice and communication between the tanks. On Heroic you need your tanks to kite, so they might as well learn. On Normal it doesn't really matter.
Traded pheremones ~20 stacks. For healing, I was beacon swapping to always have it on the pheremone kiter since they were usually out of range of other heals. I used PvP 4-set and divine purpose spec to roll eternal flames on the raid. Shaman was responsible for healing dps who were on the back legs since they were out of my range. Healing cd's popped to top people before crush, we used healing tide and ascendance primarily.
The pheremones only pass if you're within 5 yards of each other. There is enough room to move within the cleave range so you won't pass pheremones but its not easy to do, so I'd still suggest just having a few ranged dps do it. Preferably ones who don't lose much by having to be moving constantly like hunters. In our case, the lock and priest were the next best since boomkin dps is hurt much more by not being able to chain cast.
Heroism was used as soon as our hunter had the first pheremones to allow us to burn the legs down quickly the first time. After that were were basically able to keep 3 legs broken almost the entire time. Key to remember that if all legs are broken or if you can't get to the circle around the legs, just burn the body to keep damage going.
We have our Disc Priest carry it first, then pass it to the Ele Sham, then the Holy Pal, then to the Destro Lock (me). We go to 20 stacks, but also 3 Heal/2 tank. Usually still 45-50 seconds head of the enrage timer on 10M normal.
10-man heroic, our short answer is "everyone;" that's not entirely accurate, but it's close. We have a set rotation that essentially goes the tanks first, then through the healers/ranged, then back to the tanks. (Healers/ranged don't get it again: the enrage would happen before they're needed for the second time around.) Only the melee don't have to pheromone kite.
We go to 20 stacks, though there is sometimes a slight deviation (we sometimes have to wait a few seconds on that last ranged DPS before the first tank's stacks drop).