If your wife's case has already been documentarily qualified (DQ) by NVC, then that means you already paid the immigrant visa (IV) fee for her case. Can't get NVC review without paying IV fee first. So no need to pay any further fees to NVC. Depending on the consulate and their contracted courier, there could be a courier delivery fee for the passport with visa. After your wife gets her spouse visa, you should pay the $220 immigrant fee (ie, GC production fee) to USCIS, not to NVC. No fee for biometrics.
As for your stepchild, you submitted a separate I-130 petition, right? Is the I-130 already approved and the case also DQ-ed at NVC? If so, same as in your wife's case -- no MRV fee, no biometrics fee, just pay GC fee after getting the visa for the child.