First, don't let there be drama where you can help it. Not every issue is the end of the world. Granted, some issues are really important. Thus, learn to pick your battles.
Second, remember what your wedding day is about -- you and your fiance committing to love one another from this day forward. Remind everyone involved of this. It's a time for people to come together to celebrate your love.
Third, be upfront. If family members are contributing financially, be clear about expectations and who controls what. The person giving the money has the right to have an opinion on how the money is spent. You, as the person being offered the money, have the right to politely decline if there are stings attached.
Every client I've worked with has some sort of sticky family issue at one point or another, and I'm always happy to step in as an unbiassed third party when appropriate. (My mom actually tells me I should market myself as the 'Switzerland' of wedding planning.) Just keep what is important at the center of your planning, and hold on tight. At the end of it all, you will be married and that is the point. If you can't weather the storm together (don't worry, it's okay if you need a life preserver now and again), then you may want to stop and seriously think about why you are getting married.
Wishing you more bliss and less drama,
