The best wedding I ever went to (and I'm 61 so I've been to many) was a surprise.
They had invited us to see the new shed/garden room they had built at the bride's home. "And whatever else we may feel like celebrating." I interpreted that as the groom's birthday, which was a week or so away, so we took a clock for the wall of the new garden room. Invitation was for 2pm.
Well, the bride greeted us in the driveway wearing jeans, a pink hoodie and a shiny new gold wedding band. She enjoyed everyone's squeals and shrieks as they filtered in. Turns out they had been privately married in the morning with just parents and siblings present at the registry.
Beer, wine, champagne, endless platters of sandwich materials, breads, cheese, veggies/dip, pickles, olives, crisps, etc. laid out in the new garden room. Every so often her brother or someone would go in and bake another tray of pigs in blankets. Later in the afternoon some pots of chili were brought out. She had several homemade "wedding cakes" that we enjoyed off and on all afternoon. Music was via a bluetooth speaker; the bride had put together a playlist.
Job done around 7pm; happy guests left, family members helped with the clean-up and the bride and groom relaxed and finished packing for their honeymoon, departing early the next morning. I doubt the whole affair cost a thousand quid.
No one gave a shit about clothing, flowers, photography, fancy food, favours, bridesmaids and all that other folderal. She never had a hen do and he didn't have a stag. They didn't get much in the way of gifts because no one knew it was a wedding. But I can still hear the shrieks of laughter and fun that took place at that party, 20 years later. To this day she is super smug that she pulled off the surprise despite the hints in the invitation.
OP, do something out of the ordinary. Your relative's wedding will be a one-week wonder; nobody remembers those boring fancy weddings a few days later. If yours if charming, low-budget, heartfelt and (please!) doesn't suck up people's entire day, it will be a hit. I'd rather have a plate of cheese, biscuits and olives, with a couple of glasses of decent fizz, at a charming unpretentious wedding than lobster and fillet steak at some boring predictable interminable flop.
Either elope, or use the venue you have hired to have a casual, informal, charmingly unpretentious wedding. I guarantee you it will make the other one look stodgy, expensive, pretentious and obnoxious by comparison.