You will get many opinions regarding the best choice for your family between OKW and BWV. As a BWV owner, I admit to having some bias toward my particular choice, but your circumstances are very different from ours, so YMMV.
In any case, I would say BWV provides a "luxury hotel with some added features" in the studios or "apartment condominium" in the 1-, 2-, and 3-BR units with a location in the middle of the BW entertainment area. Valet parking is available, room service is available, but other food service choices are those on the BW or at other nearby resorts (Y&BC, Swan, Dolphin are all easy walks) and Epcot (a 5 or 10 minute walk). OKW units are more "townhouse apartment" style, one floor units in free-standing multi-storied building each with nearby parking and scattered about a large site around a golf course with bus stops and pools within walking distance. From BWV, you walk or take a short boat ride to Epcot and MGM and bus (or drive yourself) to MK, AK, DD, and the waterparks. From OKW, you walk or take a short boat ride to DD and bus (or drive yourself) to the rest. We really like being on the BW and close to Epcot (our favorite park) and MGM. We do little or no cooking in the room, fixing only simple breakfasts and leftovers, so being close to a lot of nice restaurants is a big plus to us.
Per night point cost for OKW are lower than those for preferred view BWV units (preferred view are about 80% of available units at BWV), and annual dues are lower as well, so your points go further at OKW than at BWV. However, if you use the 11-month window to reserve standard view at BWV, you can reduce the per night point cost difference significantly (although no grand villas are available in standard view so this does not apply to 3-BR villas).
Regarding resale purchasing: we purchased at BWV via resale. Once a
DVC member, your are treated exactly the same as if you were the original purchaser. In fact, our membership cards have the original date of purchase of the contract we bought, not the resale date. Both OKW and BWV are sold out and both first-time and add-on purchasers at either location are competing in the resale market. Right now, it appears that there is somewhat better availability of OKW resales compared to BWV, but the market fluctuates. One good plan is to decide how many points you want and where you want to buy and then contact one or both of the resale agents frequently mentioned here to get an agent to start looking for something which matches your purchase parameters. It seems that a good number of resale listings never make it to the agency web sites because there are buyers waiting who make offers as soon as something becomes available. In any case, resales are subject to negotiation. Price is an obvious consideration, but you can also negotiate closing costs and who pays current year dues. Our closing costs on a 220 point contract were $475, which I believe to be typical. Also to be considered in evaluating a resale offering is the number of banked and/or borrowed points which might be available and your ability to then use or bank any points which might otherwise expire during the year of purchase. We ended up paying annual dues on those points we would have the use of during the purchase year with the sellers paying dues on points that had been borrowed and used by them. Our original offer had the sellers paying all current year dues, but the sellers balked at this and we were buying a BWV contract at a time when the market for such was very tight. Another factor in resale purchase is how you finance the purchase. We paid cash, so this was not an issue for us, but if I had financed I would have used my home equity line of credit so interest would be tax deductable. Interest rates available through the resale brokers tend to be much higher than home equity lines and may not be tax deductable. For some buyers, the ready availability of financing from Disney is a factor which makes buying at VWL preferable to a resale at OKW or BWV.
We did not find that we needed our own (buyers') agent in making a purchase offer on the resale we bought. Both of the resale agencies we contacted appeared to be reliable and trustworthy and we would certainly do it the same way again.
Good luck with your buying decision. Keep the questions coming.
Ralph