For May, there should be good availability of villas at AKV, particularly Kidani, as long as you are not thinking value or concierge. If you do not have enough points to have the BWV reservation and also the AKV reservation, then it would be best to call MS at 9AM (EST) on the first day of your 7 month window and they can do it for you without losing the days at BWV that you want to keep. Of course, they can only adjust one reservation at a time, so you may want to have them make sure there is wide availability for both the studio and 2BR before they book one of them.
One thing to think about with a BWV/AKV split stay is that the AKV rooms will feel much bigger than the BWV rooms and the 2BR at AKV will have the 3 full baths. That could set a few up for disappointment if you start with AKV and then move to BWV. But, the activity on the Boardwalk and the proximity to Epcot and HS helps to make up for that difference. For our split stays, we often try to end the trip at AKV, as it is much quieter and more serene than the resort that are close to the parks.
Good luck and enjoy your trip!