Sexing them cannot be done visually with these fish.
Watching for particular behaviors can give you hints but your suspicions are never confirmed until your either vent them or they pair.
Since they're hanging out together and the big one isn't beating on the smaller one it would be easy to say that, yes, it looks like you have a pair. You might not though.
The slightly upturned mouth of the larger fish makes me suspicious as to whether or not it's actually brichardi. The smaller one's face looks right but it looks very thin. Put some weight on that one. With good frequent feeding and some live/frozen foods added here and there they'll be in spawning condition in no time.