More importantly, I have a cunning plan.
We do not, specifically have to be the ones taking on the Bandits now, do we?
We know Horra fears Steinarr more than anything else, the closest thing he has to being safe is the fortress he's turned his Farm into. So what happens if Steinarr's venting some bad temperment on some Acceptable Targets that are still somewhat adjacent to him?
He's going to keep his head down, and stay in his hall. He knows if Steinarr thought he was there, Steinarr would be on top of him--so he knows he's probably not made, but he's going to keep his head down until he's absolutely secured his dominance.
Which means he's not leaving his Hall. If he thought he was ready to take Steinarr down, he'd have baited him into an attack by now, which tells me that he doesn't feel ready for that yet.
Which means we have time to try and disarm the spells on his Sanctum and infiltrate it, then bring the Evidence down on him before he knows we're onto him. Effectively using his fear of Steinarr as a cloak while we line him up for the kill.
There's no such thing as a Spell that cannot be undone, and this buys us some time to work on it. He'll be on guard--but in an abstract sense of lying low as opposed to expecting an imminent overwhelming assault. Ideally, by the time he knows he's been made, we'll have him in checkmate.
But ultimately, I just feel the risk of following him into a tight, enclosed space and being stuck there until he decides to leave is too great.