The demon lvl is capped to you own lvl
it will be lvl 91
conv will be lvl 11, but can be increased by cta to make it lvl 12
You would need clvl 96 for it to be a base lvl 12 and increased to lvl 13 with cta
lvl 11, 12, 13... doesn't matter, they won't naturally break all immunity and it's only 1% difference per lvl against immunes
I'm still not 100% sure that the conviction level provided by a demon is being increased with battle command or not
For a mercenary, it will cast the aura and make it active only after teleporting around a bit, so you get a chance to apply BC first
For demons, the aura is always active. Does it stop the level 12 aura and start the level 13, like it does on a player? I don't know.