As you can see this brother and sister are peas in a pod.  Sometimes you wonder if you are going to "rock the boat" and "ruin" what is as close to perfect as you can get in terms of a family by adding another child into the mix.  In the end you have to follow your heart and trust God that the outcome will be what you are praying for.  At worst we hear "Don't copy me", "Give it back" or "MOM she/he will not leave me alone".  Most of the time though it is as in the video...lots of fun and giggles.  Mark and Marissa may it always be like this for you as you travel through life...laughter, fun, good natured competition and the ability to push each other forward to be better human beings.  You will need to lean on each other when times are tough and the world gets rough!