We stayed with 5 at BCV this summer. Yes, you can do it (I was told they allow it for DVC but not for "regular" cash). No problems with getting DDP as long as everyone is listed on the reservation. The room is too small for a chair...but my kids are all young enough that they all shared the bed. There is only 1 bathroom. They do provide enough towels. Although it is listed as linens for 4, there are more than four towels in the room. Between what is provided and doing laundry,we had no problems there.
Better for the price is AKL-Kidani. Two full bathrooms, a sleeper chair, and more room overall. BLT also had plenty of room same amenities as AKL-K. We are headed to OKW next month so we will get to see first hand how that compares!
Oh...and we really like the pool at AKL-K. Yeah, BCV has the sandbottom (which is why we stayed a couple of days there), but I actually found the sprawling layout a little overwhelming with young kids. Get to the AKL-K pool and be one of the first to open the slide in the morning and there just might be a little extra magic!