Mierce Miniatures

I really like the look of some of the Bane Legions models, and I would like to use them in my Darklands gaming, but I don't know what kindred any of them would be aligned to, or if they even have muster sheets..

I assume I could use them like Sell Swords, but not sure..

Can someone offer some advice..

They don't have muster sheets and I doubt they ever will as they were never intended to be included into darklands. but no-one is stopping you from using them as count-as models in your hosts as long as their base-size corresponds to the Darklands model it represents.

Im not sure that would fly in competition's though, as it's pretty much what you have on the table has to be what it is without exception, so if its a Guthwulf, it has to be a model of a Guthwulf..

That will be the only way to use them in a game of darklands, as other than using house-rules (which, if you're talking about competitions are out aswell) they won't be getting rules.
They are sculpted / converted with warhammer in mind, and they don't have a "place" in darklands as a world.
Now, I don't know which models you're interested in, but there are plenty of banebeasts that have a lot in common with the models they were based off of. And even if they were original sculpts like Three-Face, he could work as a Goz-Horror or a Kill-Thing.
Ork (c)s and elves don't exist in Darklands, so those models are out either way.