There are no studios that allow 5 guests at BWV or any of the other WDW
DVC resorts. There used to be a 'studio plus' offered at BWV that had a little deacons bench that might be suitable for a small todder, but I don't believe that's offered anymore.
AKV, BLT and OKW one-bedroom villas have an occupancy limit of 5 persons plus one child under the age of 3. There's a sleeper chair in the living room along with the sofa bed, so there are actual sleeping spaces for 5.
Member Services is
currently allowing guests to book 5 persons plus one child in a one bedroom villa in these DVC resorts: BWV, BCV, VWL, SSR. Since the official occupancy for these resorts is 4 in a 1-BR, I would not buy with the assumption it will always be that way - it could change tomorrow.
If you do book 5 in a one bedroom at BWV, BCV, VWL or SSR, be aware that they won't provide bedding for the 5th person. You would have to bring your own air mattress, sheets, pillows, etc.