I decked my 1436 Monark Jon, and here's what I can tell you. It's not rock solid steady like a pontoon boat, and if you have 2 grown men and a 16 year old teenager all get to the same side, you will feel like it might tip over, but I wouldn't make mine any smaller. I kept a little "pit" area to keep my kids in when I go out ( I have 3 kids age 4 and down). If you're clumsy, no matter how you slice it, a 14ft jon is going to be awkward at times, but I've taken my family out before mods, and after mods, and honestly, it was easier to do after the mod then before it. One thing that will help the stability is making your seats where you can remove the pole and just insert the seat into the base. You will have a lower center of gravity then (like when you're driving) and be able to add the height when you want or need it.
Henry is right, everybody's sense of balance is different, and another thing that will help you is getting a transom mount trolling motor. Keeps the deck free of cables that could trip you up or take up room for other things.
I think this is going to be a great build, and you're doing a great job. You have a great boat, and a great family. I know from experience what a blessed man you are.