You could possibly try Tag Boosting.

You need at least two toons grouped, your five RAF toons make their own group.
And the boosters have to kill entirely with pet damage.
The lowbies will get full experience for anything they tag.

I was using this method to take toons from 60th to 70th in Borean Tundra, killing rhinos.
Totems are considered pets.
My method was group two toons (you have five), wear all +Stamina gear and tag a lot of mobs via AoE.
Then have the Shammies drop 3x (you'll have five) Magma totems.
Plus drop 1x Stoneclaw Totem (the Taunt + Stun totem) on round-robin.
One of my shammies is dual spec, so did Earth Shield on the lowbie.
I did 60-70th in an extremely boring afternoon, but it was 10 levels in under 6 hours.

The trick would be finding areas with massive numbers of mobs, and fast respawns.
You'd want mobs who are +3 to +8 (+3 to +5, is ideal) levels ahead of the lower toons.