how to make your wedding photo looks more natural
In fact, the posture cant be stiff, however, the face expression will be.
If the posture is not very natural, it is not the about the posture, is some details instead, the most posible part is the hand guesture.
In realy life, many people prefer: "act like normal, then take the shot". This point may not be true, because the realy life is so real, it might be not that aesthetic beautiful.
Take hand guesture as an example, many couples are holding hands as interlocking. but on the photography, it looks a giant riot. It's ugly and not natural.
Another example, if some part of your body influene on your natural photo result, it must be elbow. 90 degree elbow angle is a right angle. This unnatural angle make photo very unnatural. Those details is very hard to notice when you are positioning. Let photographer or your friends help you.
Symmetric photo is special case, heads, shoulders, or legs, is on the same level will result in not natural photo. so, void symmetric postures.
The conclusion is relax yourself, try to NO be symmetric, some experienced photographer will remain these details.