The horses share a trainer or common ownership. The coupling is done to prevent any chicanery or to alert the bettor that one horse may be helping the other. You don't see it as much anymore due to the rise of super stables, e.g. Pletcher or Baffert may have three horses in a race, and the tracks want more betting interests and so get waivers from the state racing board.

_________________
Anybody here seen my old friend Bobby?
Can you tell me where he's gone?
I thought I saw him walkin' up to The Hill
With Elon, Tulsi, and Don

The race in our fantasy league had it yesterday. Thanks for the explanation.

So if 1 finishes first, and 1A finishes second, how does that work? Ignore 1A and whoevere finishes third is really second?

Correct. For purposes of the gimmicks you would ignore the second one.

_________________
Anybody here seen my old friend Bobby?
Can you tell me where he's gone?
I thought I saw him walkin' up to The Hill
With Elon, Tulsi, and Don