You bride-to-be will be coming into the marriage owning a house. Louisiana is a community property state, which in general means that any assets or debts acquired after marriage are considered by state law to belong to both spouses. However, property or debts acquired separately before the marriage remain separate after the marriage. Unless you do something silly -- like changing the deed of the home or adding both names to the mortgage -- the marriage doesn't change the ownership of separate property. So your credit and debt situation will not affect the home unless the two of you want to share everything including your debts.
My guess is she's smart enough not to go down that particular aisle with you. However, there is nothing wrong with you and your fiancee sharing the mortgage, tax or insurance payments on the home after you are married as long as she remains the owner of the home. Once your debts are history, and your marriage has proven itself to be not her first, but her one and only, then she might consider placing the home in both names for financial planning reasons.
Because your fiancee and her family have concerns about your debt, I recommend that you get a plan in place to pay off the debt you owe as soon as possible. It goes without saying, but let me say it anyway: You must stop accumulating additional debt. Also, it is a good idea to have a thorough discussion and come to an agreement before the big day about how you will handle your finances once you are married. Money is one of main reasons why marriages fail.
The decision of whether or not to sign the prenup is up to you and your future wife. If it is important to her (not to her parents) that you sign, I recommend you have your own attorney review the document before you sign. In my experience, prenups are hard to enforce and go against what we all pray will be a lasting, lifelong commitment to another person. Only you can decide if signing is in your and your fiancee's best interests.
As a father-in-law myself, I can't resist giving a little advice to your fiancee's parents: Your daughter is making a decision to marry someone, and I strongly encourage you to support her. Rather than trying to protect her from her husband, support them both in any of a hundred positive ways. Suggesting that a lawyer accompany them on their honeymoon isn't one of them.