For a family of four with a fifth on the way, you might want to consider any of the resorts that the one bedrooms sleep five. That would be AKV, BLT and OKW. BLT is not a bargain for purchase even on resale nor to stay there. It pains me to say that because I love BLT, but it's true.
Like others have said the villas at OKW are the largest and the points cost per night are low. AKV has value villas that the point cost per night is slightly lower than OKW, but they sleep four not five. SSR would cost less to purchase a resale than OKW and AVK, but the point cost per night is higher. BTW the standard/Savanna view rooms at Kidani Village have two bathrooms. Whereas the value and villas at Jambo House all have 1 bathroom at AKV.
I don't think you'd go wrong with choosing AKV, OKW or SSR. Just keep in mind that a member of your family will have to sleep on air mattress (that you provide) at SSR once the baby gets old enough for a bed.