Now, if I were to take in this intrepid trio to an instance and run them through with my 80 druid (on my fourth account, not tied to RAF), will the three still garner the RAF bonuses?
To answer this originaly question:

Yes they would get the 300% CP Bonus from RAF, because as you described only three of them are linked and most importantly the account of your 80 druid is not linked with one off the RAF-Accounts. SO for all three RAF-Accounts als long as the mobs are not 'grey' they get the 300% bonus.
Only think you must keep in mind, is that because of the level-difference of your 80 to the other 3 the XP they get is reduced (but this is always the case with 80-boosting, RAF or no RAF)