How else can you help bring the in-laws together over the wedding preparations while getting the wedding you want? Here are some ideas:
For the bride and groom
This is your wedding. If you have strong convictions on a specific issue, say so -- or forever hold your peace.
Establish your identity as a couple by sticking together and making joint decisions.
If you are paying the entire cost of the wedding, you can theoretically have things exactly the way you want. But be careful what you wish for you may get it. Instead of being a big baby, consider giving in on small issues to establish good relations with your in-laws from the get-go.
If you are not footing the bill, be prepared to compromise on significant issues.
No matter who pays for the wedding, the wedding couple ought to discuss and decide on such important issues as the day, time, religious or secular service, customs, location, guest list, music, and so on.
Under no circumstances act as the negotiator between the two sets of parents. Even if you are the chief negotiator for the UN, it's not your job to arrange peace in our time among the in-laws. It is your job to get married.
For the parents, parents-in-law, sisters-in-law, and brothers-in-law
Remember that this is your child's or child-in-law's marriage, not yours.
Be there to help the bride and groom have the day they wish to have, not the day you think they should have.
Even if you are paying for the entire wedding, be sure to consider the other set of parents involved.
Respect other people's customs and culture, even if they are radically different from your own.
Understand that you don't have to love this stranger who has stolen your child. All we're asking for here is a little respect. Ditto for the other set of parents-in-law and all their relatives.