The stat values aren't final- I might lower their HP a bit, and take some edge off Beguiling Blade because "hits twice and lowers Block" is fundamentally a strong effect already, and even more so with Poison tacked on. They're still going to be pretty tough, but fortunately, Brill will have help for this one. I didn't include him in this screenshot, but he's got a skill that can mess them up. (There's also a few specific items and equipment pieces that give them trouble.)
They might pair up with some of the other enemies in the dungeon, but anything beyond two of them is definitely going to be considered a miniboss.
This place is the first dungeon of the update. Don't worry- it'll make sense when you get there.