It sounds like your thought process makes sense. Having 2 beds for 2 couples is much better than one couple having to sleep on the sleeper sofa.
The newly refurbished OKW rooms look very nice, so i think you would be comfortable there and they would be much larger than the PO studios. 9 nights is a long time to be in a small space, no matter how well you get along. Plus you have the boat to DS.
Have you calculated getting TiW? We did this for our trip in April - 7 of us with at least 1 TS meal per day. It definitely saved us money and we were able to use it for another trip. I'd imagine you would get some savings even with 4 adults dining. So if you think you would be back again and could use TiW then that might work out better than the "free dining".
I think the space you get at the deluxe OKW studios would be a huge bonus when traveling that long with in-laws (just saying for your wife's sake).
To save this much i don't know if it would be worth it to be stuck in a small room. In POR there aren't even doors to the sink area of the bathroom. The only privacy is in the tiny toilet/shower area. Plus in a
DVC room you will get the fridge/coffee maker/micro - which might be nice if you just want to store a few items for a quick breakfast. We stayed POR for one night with just my DH and DD and it was nice but DVC rooms are definitely a big step up.
I just looked - to get a 2BR at OKW for 9 nights in September it would be 275 points -- you could borrow some points to really splurge and have space with your parents. Or just shorten your trip to 7 nights for 217 points.