For you AKV -- you normally stay at VWL and are used to being at that end of the resort. AKV is very different in theme, culture and the incredible savanna. You and your family have the opportunity to talk with cast members who come from a part of our world that many don't have an opportunity to visit. Stay at Kidani for larger better designed villas.
For your BIL and family -- they might prefer BLT for a first visit with young children where they can see the MK lit up at night, fireworks, the floats on the lake, the monorail, etc.
If your trip is long enough consider a split stay and enjoy both. If not, go with being the good host and go to BLT. Then enjoy AKV on another trip.