If what they want is reasonable, don't fight it. That makes your job easier. But, if what they want is unreasonable, be honest with them, but, by all means, be tactful. Also, this will help you with your planning so they won't be in your video, and you won't show up in the photos. This brings up the subject of planning.
Planning is all important when it comes to wedding videos.
You will be producing something that the couple will want to view over and over, that their family and friends will be seeing. It's your best advertisement. So, you will want it to be the best it can be. If you know what the ceremony will be like ahead of time, and what special shots the couple and family will want, you've got the ball in your court. Be sure to attend the rehearsal, so you can set your equipment up and plan your camera angles.