I would rather have a Large Steampunk Arachnid or a Soulstone Miner. They are more useful than the swarm (except with Ramos) and the Victorias need more than 3 soulstones to survive.
Necropunks are good objective grabbers.
Rotten Belles are good for Lure.
Ryle is good for ranged support.
Crooked Men are good for area denial (and great combined with rotten belles)
If you're looking to bring his avatar, the riders are necessary.
If you drag one Victoria away, and they haven't already activated, they can just use Sisters In Spirit to push them back together. The Avatar can only form if both Victorias are still in the game.
Once you kill one Victoria, the other loses a lot of her usefulness. At 7 wounds, they are fairly fragile once you force them to get rid of their soulstones, so focus on killing one of them (preferrably the one with two swords).