I actually have some advice to give. After being very active in the boards I have noticed many people with family issues. It has had me thinking and now I have some advise for those of you that may need it.
I should preface that no one has to agree with me, I am just offering a professional opinion based on general circumstances and so I hope no one will post negative comments about the fact that I offered this.
In situations where a parent (parents, friends, brother, sister, aunt, etc...) is giving you grief I think you should BOTH sit down with them to talk. Maybe the "blood" does most of the talking, but you/they should be there. If you/they are not there it will create the standard that it is you/they against "them" and their son/daughter is only a mediator.
If you are together you set the standard that you are all family now, which you are because that is what happens when people get married. You also set the standard that you and your fiancé are a team and that you both feel strongly about this topic, that you both agree on this topic, and that you both care about them and want to resolve the problem.
By avoiding people and sending some one else into the "battle" you also create an unfair situation for the person in middle, in which they now have two loved ones disagreeing and they have to work alone to resolve the problem, possibly disappointing one of them.
Even when it is not case, avoidance sends the message that you do want to deal with that person, thus offending them and setting the foundation for a poor relationship in the future. One in which they may feel unable to approach you about other problems or unable to even trust you.
I hope you will all reconsider the advise to "deal with your own parents (children, siblings, etc...)." And wish you all the best with your wedding planning!