There's also an /aid command.
I'm 2-box an Ironbreaker (Sanctume, main) and a Rune Priest (Spiritstone, 2nd)

On the Ironbreaker:
"Target"
/target Sanctume

"Invice"
/invite Spiritstone

On the Rune Priest:
"Assist"
/assist Sanctume

"Target"
/target Sanctume

"Follow"
/target Sanctume
/follow

"Self"
/target Spiritstone

"Aid"
/aid Sanctume