If B and C are linked (the link from A does not matter), they'll receive the bonus experience if:
- i) They are grouped and close to each other;
- ii) They're within +/- 4 levels of each other;
- iii) They're both level 59 or lower.
- iv) The mobs or quest is not gray to either of them.

If it is just the two of them, you might receive 300 experience per kill (divided two ways, for two in the party), or slightly more then 150 each (party bonus adds a minute amount)... say 152 exp each.

Without RAF, they'd be getting 100 experience per kill, or slightly over 50 each.

With a level 80 in the party, and no RAF, they might get 5 experience per kill.
With a level 80 in the party, and RAF bonus, they might get 15 experience per kill.

But the 80 is worthwhile, as they can gather a hundred mobs.
And kill them in less time, then a lowbie could.

For levels 1-10, kills are basically worthless, and its just that you do quests incredibly quickly and easily.
Once your toons are high enough level to be boosted, the 80 really speeds your progress up.

A level 14 elite, in an instance might take your two toons 45 seconds to kill, at level 12.
And then your mana is almost gone, you need to heal, etc.
And you might make 500 exp each on the one kill.

Conversely, with the 80th in the party...
You have half of the instance pulled in one go.
Which takes 3 minutes to do.
And you get 50 exp per kill, but drop 80 mobs at once.
Another 3 minutes later, the other 80 drop.
And you've made 8,000 exp each... in the time you'd be lucky to have made more then 2,000 each.
Plus there is no chance of dying on the lowbies, with the 80 killing level 14 elites.

You can boost safely and easily to 60th, like this.