Based on the fact that Marsh gave Wax that book we can assume The Set know about Hemalurgy.
Now the Set are a smart group, if they just wanted to make Inquisitors they could have just spiked any misting or ferring and be done with it. So why kidnap those specific women?
Simple, the Set are going to turn those poor women into Inquisitors.
Why you ask? Well it's as Marasi and Wax feared, they will be used for "breeding" but not for an army like they suspected.
The Women will be be used to breed the second Lord Ruler.