Hi Cal King,
You should be fine either way on an adjustable bed and I would base your decision about whether to split the layers on your discussions with the manufacturer or retailer you are working with about whether it would be beneficial to have split layering.
Based on your weight you would both be fine with 8" - 9" of latex in most cases. Post #14 here talks about the potential benefits of more layers or thicker mattresses.
Both 9" and 12" are in the range that would conform well to an adjustable bed although the 9" will conform a little more “exactly”.
Phoenix