You gotta be kidding me; get a load of that chipmunk!
Who are the other guys?

I second Carl's comments. Who are the three unknowns in the poster pic, studio musicians?

No! Those are just the other guys in Hourglass.

This is from the Natural Fire website:

Formed in Decatur, Alabama in 1967 from the ashes of the Allman Joys, the group was fronted by Gregg Allman (vocals/organ) and his brother Duane Allman (guitar). Paul Hornsby (keyboards), Mabron McKinney (bass) and Johnny Sandlin completed the original line-up, 'discovered' playing juke-box favourites by the Nitty Gritty Dirt Band and their manager, Bill McEwan. The Hour Glass then moved to California, where they became a popular live attraction. Although their debut album consisted largely of pop/soul cover versions, it did include 'Cast Off All My Fears', an early Jackson Browne composition. However, the set was essentially a vehicle for Gregg's voice, and with session musicians replacing the group proper, the results bore no relation to the quintet's own ambitions. Jesse Willard Carr replaced McKinney for Power Of Love, in which several 'southern' soul songs vied with group originals. Once again the album failed to capture their full potential and in a final act of defiance, the Hour Glass booked themselves into the fabled Fame studios at Muscle Shoals, where they completed a searing B.B. King medley. When their label rejected the master as unsuitable, the quintet decided to go their separate ways. Gregg and Duane later formed the Allman Brothers Band, an act later produced by Johnny Sandlin. Hornsby became manager of the group's Capricorn Sound studios while Carr enjoyed a lucrative session career.

http://zebro.everperfect.com/allman/others/HourGlass.html

I know that Duane asked a couple of them to be in the Allman Brothers, but they were tired of trying to hit the bigtime.