True, did they send Solo?, was it Rikishi? are there other elders?
Yeah, after Solo's debut Roman said "The elders may have sent you, but you answer to me now" and Solo did the whole "I acknolwedge you my Tribal Chief" thing to complete initiation.
It's all just speculation, but everything they've hinted at and shown about Solo says the following from a kayfabe perspective:
1. He didn't grow up the way the Usos grew up. NOTE: the Usos and Roman are roughly the same age so they've been de facto brothers. So based on the timeline. The Usos and Roman would have been off to college, pursuing football and eventually the WWE during Solo's coming of age/rise to manhood.
2. This is further driven home by the fact that in the ring, though they all share some of the same foundational moves, holds and such, Solo is a modern-day version of the Wild Samoans/Umaga. He doesn't wrestle like the Usos and Roman. So it can be implied that with no notable male influences around him to steer him otherwise, the elders could have molded Solo into their image.
It's not out of the realm to believe that Solo is there to be eyes and ears for the Elders but at the end of the day, he's loyal to the throne and not necessarily who is on it.