Were the other trainers from Pallet town ever revealed? We know four trainers started in Pallet town. Three with one of the three original starters and Ash with his Pikachu. Apart from Gary, were the other two trainers ever revealed in the anime? And was it ever revealed who got which specific starter Pokemon?
First, the things we know:
Ash got late and had to pick the reserve Pokemon Pikachu. The other 3 starter Pokemon already got picked, one of which was picked by Gary. At the end of the series, you could see that Gary picked Squirtle.



So the question is, who picked the other 2 starters and where were they mentioned?

Your question really inspired me to find a answer. I found answers on multiple sites.

On reddit


  In the series, Ash and co. encounter a Charmander that was abandoned
  by its owner. We might infer that the original owner was one of the
  other two Pallet Town trainers. In addition, the Bulbasaur Ash and co.
  encounter was raised in the Hidden Village, which the article linked
  states was a haven for, among other things, abandoned Pokemon. So it
  appears possible that the other Pallet Town trainers also abandoned
  his starter Pokemon.


On serebiiforums


  These two mystery trainers' sole purpose in the anime was to be a plot device so that Ash would miss out on all 3 standard starter Pokemon and get Pikachu.
  
  Gary got 1 of them (and it wasn't revealed until the very end of
  Johto) and for marketing purposes, Ash had to have Pikachu as his very
  first Pokemon...
  
  So they invented 2 other trainers to get the remaining Pokemon... and
  they were referenced a few times until after Ash got the Earth badge
  and returned to Pallet town. That was when Oak said that the "other
  two" gave up and flunked out. Thus writing them out of the show
  permanently... never to be referenced again.


So it seems that these 2 mysterious trainers were just there to lose their starter Pokemon after a short time, so Ash could find them and train during the series, the 4 most favorite Pokemon of every kid. (Squirtle came to him from the firefighter)

I think the 2 trainers weren't meant to have a big part in this series. They were just needed to give Ash the rare Pokemon everyone wants to have.

But this is just my personal opinion.