You got me thinking.

Neither boy is going to roll the Kayak. With their low center of gravity they can't even make it roll by putting their head in the water.

I think I will make the seat size for my back-side and use two sets of hip pads as you suggested. I hav a back band and can use it to adjust them forward in the boat for trim.

On other thing -- several of the articles on seats talk about 12" front to back. I think I will use about 18 so I have a bit of support, and that will give the boys some adjustment room.

Thanks for the comments.