Unwanted guest rant - dont know what to do Help!

We sent out STDs in November and I had someone tell me that she and her husband will be attending the wedding. A STD was sent to the couple as a request from my parents (whom are paying for half of the wedding) but it was more of a "courtesy" than them wanting them to actually attend. We were all hoping they'll say no.


Let me tell you why. My family (parents) is very involved in their church and while they dont engage in any drinking or partying of the sort my wedding will have an open bar and music. Some of my younger cousins and aunts and uncles are not as involved and they will most likely want to have a drink and/or dance. I KNOW for a fact that if this lady who already confirmed attendance goes she will be going back to church and report on everything that went on at my wedding which will result in lots of talks. I personally don't care what she says or thinks about me I dont go to their church but I know that she will prevent the rest of my family from enjoying themselves which is stressing ME out.
My parents knew this but they felt bad not including them in the wedding (given that they are very involved with the church). Which is why they asked that they are invited but we were hoping they'll say no. Specially because I'm having a Thursday wedding and they have service on that day.