This is definitely a conscience matter. I dealt with this many times over the years that I was an active J-Dub. My husband was a non-believer and I attended many weddings of family, friends, and coworkers of his in churches. I did not tell others in the congregation about it because I had learned a long time ago to keep my business to myself, there were those who would always judge and make an issue of things.
A pioneer sister cleans house for me once a week. She knows I don't go to the Hall any more, but she doesn't know I no longer believe in it. We just don't talk about it. Her husband is an elder. About a year or so ago, they attended a wedding of a family member in a church. She said she told her husband they should go because they did not do the holidays with them and she was afraid if they didn't go, the family would think they just didn't care about them.
My youngest son got married in January at a Presbyterian church here in town. My mother, brother and sister-in-law, and two nephews and their wives, all witnesses, chose not to go the wedding because it was in a church, but did come to the reception. My sister and two of her sons who are witnesses and her daughter-in-law who is a witness did come to the wedding even though it was in a church. Our mother tried to put a guilt trip on her over it and convince her not to go, but my sister said to me that she read the Watchtower article they were going by and it was clearly a matter of conscience and that her conscience would allow her to attend. There are a lot of hard feelings in my immediate family toward the ones who would not attend the church wedding. The pioneer sister who cleans for me said to me that there are many witnesses who would never step foot in a church for anything.
That being said, the problem you are going to have is that you have been a witness and have faded. Were you baptized? Particularly if you were baptized, there may be some who would not attend. But you need to be upfront with everyone about where the wedding is being held. Anway, congratulations. I wish you the very best.