(breathe in)

since you've already RAF'd account B using account A as the vet, you cannot use your 70 to boost any toon on account B anymore (see pros and cons: http://www.dual-boxing.com/wiki/inde...Example_Setups) and quoted from a blue post aka Recruit-a-Friend - Ultimate FAQ! (post #2, 3rd dot point):
If the mob is trivial to either character, no experience bonus is earned.
  • This means that if you have Player A (level 50 veteran character) grouped with Player B (level 30 RaF character) and they kill a mob that is level 32, since the mob is trivial to Player A, no bonus experience is awarded.
for your current setup (which is, account A linked to account B) i would suggest you reroll another set of toons (1 each on accounts A & B) and just quest with them (refer to RAF Questing entry in the wiki) as the difference between questing and boosting is marginal and some argue the point that questing (if done right ofc) is faster than boosting. so if you decide to do this, i suggest reading Horde and Alliance Multi Boxing RAF 1-60 Leveling Guide and following the suggestions there

with regards to the previous reply by elsegundo and probably an answer to your OP - what he's saying is that if you decide to get another account (account C as you call it), you should get account B to refer it and not account A. what will happen then is something like this:

-toon A (level 70 booster living in account A) + toon B (level 10 toon living in account B) + toon C (level 10 toon living in account C)
-they all go to deadmines and have a picnic with some ninjas and pirates
-toons B and C will get 300% xp - why? because account B referred account C which means the RAF triple experience benefit is in effect

...but account A being linked to account B means that toon B shouldn't get triple xp because of toon A being lvl70 and toon B being lvl10. that rule is currently being ignored by the system and i am not sure if i could be banned for posting this (so, apologies) but they do know about this issue. below is a blue post within the earlier linked post (RAF ultimate faq):
Let's say we have Account A with a level 70 character, Account B with a level 1 character and Account C with another level 1 character, all three characters are grouped. Account B and Account C are linked, will they receive triple experience?

  • A: Bonus experience should only be granted if the experience is not trivial to anyone in the group. Our Quality Assurance Team is looking into reports that some of these restrictions are not consistent and hope to resolve the issue soon.
so i would advice against doing it this way as you may get banned or the levels gained using this method may be taken away when they resolve the issue.

(k, can breathe out now)