As above there are 1 bedrooms that only hold 4, but it can get even more fun when you start talking about fast pass selection at 60 days and if you are considering the dining plan. You may already be aware of the following (I learned the hard way)
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The dining plan requires all members of your party in the same room to purchase the dining plan for the duration of stay.
You can book dining at 180 days plus the length of your stay, but I am not sure if all names have to be on your reservation at that start date. (I would check on that), or maybe someone here can answer that.
Also, you will be able to book fast passes at 60 days for the 5 of you, (as the children will be on your reservation), but not your son and daughter in law. Their 60 day mark will begin 4 days later.
I am not an expert and would check how these things work in advance. If the the information above is incorrect hopefully someone here on the forum can correct me.
Regarding resources, we are also DVC members and I have found the DVC member services staff to be incredibly knowledgeable. An example of what they can do is- we are having a split stay in December due to room unavailability, and when the 180 day mark to book dining came I was only permitted to book the first 3 days of our stay (despite no break in staying on property) and the DVC staff were able to make the reservations for the second 3 days for me at the 180 mark. Disney dining does not recognize the 6 contiguous days when you have a split stay.