We are a party of 6 also I have never liked the idea of have 2 separate room since it is not guaranteed they will be connecting. We just recently stayed at AoA in a Cars suite (August 2016) for 8 days and it was great for our family of 6. The whole package was $4500, so absolutely you can do it for MUCH less.
The next trip we have planned is for November of 2018 at the AKV, and we rented DVC points because we have more people coming this trip, 12 total so we are getting a 2 bedroom villa and studio. We have rented from Dave (
https://www.dvcrequest.com/) several times in the past, then we bought a DVC and subsequently sold it, so now we had to rent points again and it was still a great experience dealing with Dave and his team. The best part of the 2 bedroom vills is they will sleep 8 or 9 so you would have room for the nanny if she was to come. The downside is you can not get free dining, but you can pay extra to add it on if you want.
You really do have many options, but it totally depends on what you are looking for:
Option 1 - 2 Standard Rooms - You are not guaranteed that you will get connecting rooms but you should be able to get the free dining, and you will technically have room for the nanny. (Ball Park Price - I have no idea as this is not an option for our family)
Option 2 - Family Suite at Art of Animation - Can sleep up to 6 and your family will all be in one room and again you should be able to get the free dining but NO room for the nanny unless you want to get her a single/standard room. (Ball Park Price - $5500-$6000)
Option 3 - Rent DVC Points and stay in a 2 Bedroom Villa - Can sleep 8 or 9 so you will have room for the nanny but you can NOT get the free dining. (Ball Park Price - $6500-$7500)
Option 4 - Pay Full Rack Rates for a Suite / Villa from Disney - (Pall Bark Price - $14,000, I would never do this option)