We have an obligation to at least warn the Nal outpost of what we've seen on the ground and above. The ferel scouts have shown they can get into the outpost and out without problems and are well known to the powers that be there thanks to our previous visit (infamously so). I would say our best course is send them a warning with what we know, try to determine exactly who is manning the other ballista, and if they are enemies neutralize them. We have climbing gear, auto weapons, stealthy type warriors, and lots of rope. Our other forces, the golems, the airship, and regular armored troops, would make a devastating ambush attack on any force attacking the Nal outpost if one was needed, provided one was needed.
If I knew what I was doing I'd be dangerous.