After taking a 2nd look at your gun, it appears that yours is a little different from mine in that mine has a 2nd underlever (flush with and under the one that opens the barrels) which when rotated to the left allows removing the barrels. That notwithstanding, I still believe your gun is a either a Lefaucheux or at least a Lefaucheux knockoff.
I have inserted (below) a picture of my gun with the barrels removed and both levers extended. As you can see they are essentially the same except for maybe the 2nd underlever on mine which removes the barrels.
It was one of four SxS doubles that my father-in-law liberated from the Germans during WW2. I inherited them when he passed some years back.