My vote would be to go for MFW 1st for dd. I think she would be way too bored in K. Does ds really need a full curriculum? Maybe he could join in for some of the fun--dd could read the Bible reader aloud to him--but you could focus on reading and writing with him using other materials.
I used the MFW 1st Bible materials--stories from the teacher's guide, Bible reader and student Bible notebook--when my dd was five. I had purchased it way early--I'm getting better about that--and then changed my mind about using it. I had pieced together a course of study for her--BJU Math 1, WTM science plans for 1st grade, Primary Phonics, copywork, etc. I could never find a Bible program that I liked, so I pulled MFW off the shelf and looked at it. I added it in and it was the highlight of our year.
I would consider adding a math, though, if your dd is doing any simple math already. I wasn't impressed with the math portion, which is what deterred me from using it in the first place. It really would have been fine for us to just use it with the addition of a math, but I had already gotten us into another routine, so we just added in the Bible/history parts. The Bible history is a great pre-cursor to Ancients. Here is a blog post I wrote about using the parts we did. The author does a fantastic job with the Bible stories--not dumbing them down or leaving out important points. The process, as I say in the post, of hearing, reading, drawing, writing is fantastic.