You are an adult. And adults set boundaries and talk about their feelings.
Make sure your parents know that you and your fiance have full control of YOUR wedding.
Let them know that it’s important to you and your fiance that your wedding speaks to your authentic personality.
You’re going to make the big decisions on your own.
You don’t need to prove anything to them. Of course, your parents will try to intervene, but show them that you can handle any problem.
Once they see that their “baby” has grown and can handle life and all obstacles, they will probably take a step back.