You have an initial account.
It can be the booster or one of the lowbies who will be boosted.
Call it "A".

From the account management in A.
Send yourself an RAF invite email.
Use the emailed code to create account B.
Then upgrade B to a retail version.

Log into account B.
Send yourself an RAF invite.
Etc.
Basically ensure the chain is:

A -- B -- C -- D
Or however many accounts you are doing.

When you receive experience it will read something like:
Received (322 experience; +300 RAF, +22 Group Bonus).
If you see "x" RAF bonus, across all toons, then the chain is set up right.

With only 4x level 20's in the group.
You might receive 900 experience from a level 27 elite.
Add in the level 80, and you should get much less exp.
Maybe 300 experience after the RAF (which would be 100 exp, without RAF).
You should still be getting the RAF bonus.

The level 80 is a good deal though, because without the 80, you could kill maybe 2 or 3 elites at once.
And in 10 minutes maybe down 10-12 mobs.
The 80 can handle 30 elites at once, and in 10 minutes clear the entire instance instead of only 5% of it.

If the link is: A to B to C to D.
You should be getting RAF with or without an 80 in the party.

To get RAF.
a) You need to be grouped with a toon which is directly RAF linked to your account.
b) Be within +/- 4 levels of that toon.
c) Both of you be level 59 or lower.
d) The mob be at least green to both of you.

Even if you were A -- B -- C -- D
And had a level 80 on A, but level 10's on BCD.
You should get RAF.
The A -- B link would not qualify.
But the B -- C would, and that is all B needs.
The B -- C -- D link is good for C either way, and D is fine because C -- D is good.