Make it as clear as a bell, you are their Photographer and the BRIDE is the sole boss at the Wedding, regardless of who is writing the check. Her wishes are the ones that count. 

The latest legal contracts and agreements for weddings stresses and reinforces that during the time and at the venues of the wedding, I am the sole professional Photographer there. 

Thus, this reduces legalities to only two people if it comes to that. You and the Bride, other parties are listened to, but don’t count. Learn this point well and spell it out in WRITING. That’s the only thing that counts and wins in COURT.

It’s a two way street and as long as I have NO interference, I have NO objections to the other folks shooting pictures. This is a happy compromise, for all parties. To tell them no one else can take pictures are foolish and in some cases can cost you the job. 

The giving part is you will make sure the guests get pictures if they work with you. Explain it from a standpoint of cooperation, not one of starting a conflagration or bushfire you have to put out later.

You are the insurance agent, not the town bully. Photographers are starting to charge by time rather than exposures because all weddings drag as adjustments are made and “going over” is part of the game. At no time lose control of what has to be done.

You were hired to do the job and not to have to run interference with Uncle Herbert. Especially after Herbert has had a few. Uncles sometimes do this. That’s because Uncles are fathers too. And it’s the Mothers that planned this shindig.

The key is you are the one who is responsible and that should be clear to the Bride that you are the only and official photographer for the occasion. It is not meant as a power play, it is meant to protect the Bride’s interest. Things happen quickly at Weddings especially today with all the booze, coke, meth, some grass and most good photographers can handle this ever changing situation.
You prefer that everyone with cameras please respond to you as to when they can take their pictures as in the case with most weddings there is a schedule to adhere to. This will make things easier especially when a wedding is running behind schedule as almost everyone for me has in past forty years.. Brides are expected to be late and it is well within their rights. Trust me.