I have two theories.
1. The first one was in Thor I believe. And that one was likely a fake/model because Thanos already had the real one. Or at least that's what I think.
2. Perhaps they have one Gauntlet to counter the other.
If the first theory is true. That could mean Odin knew of Thanos from the beginning but could not stop him from taking the real gauntlet. Thus, ashamed, created a fake one to hide his weakness. This might come to light in Ragnarok and/or Infinity War and create a conflict between Thor and Odin.
If the second is true that means the first one may run on the powers of the six Infinity Gems. The second may run on will of the 6 heroes.
Captain America-Time
Starlord-Space
Doctor Strange-Soul
Captain Marvel-Power
Spider Man-Mind
Daredevil-Reality
The Big 6 of the MCU. Or it could be the 6 teams.
Original Avengers
SHIELD
Defenders
Gaurdians of the Galaxy
New Avengers
Everyone Else or Inhumans
I don't know. For me the first one makes a bit more sense.