If you can see the venue first, I'd suggest visiting to get an idea of the lighting and if your flash will be enough (or looking online to see how it's usually lit) since the lighting really matters. I personally hate relying on flash since it's distraction to others and you have to worry about angle, bounce, reflections, and recycle time. (Mostly since it's distracting though.) Also find out for sure if they've hired a pro photographer.
If it's bright enough I'd recommend the 18-135 by itself since it allows you to take long, short, and 'macro' shots without changing your lens. For the wedding ceremony itself it's also much quieter than a screw drive. The convenience of the zoom range is extremely handy, the main issue is if the venue has 'subdued' lighting (or dark and gloomy depending on how you look at it
). Same with the 55-300, but I would pick the 18-135 fist if you really don't want to change lenses.
If it's dark, I'd definitely say use the 31 and keep the 15 available in case you need it (eg: if you want to get a shot of the whole head table at once). If you find out there isn't a pro photographer you might also want to bring the 105 macro to take some pictures at the beginning such as her dress details, shoes, rings, centerpieces, decorative details, etc. It sounds like a very distinctive event, and years from now these pictures may be worth more than a thousand words when they try to explain it!
I recently had my 18-135 / K-3 at a wedding and it performed wonderfully in the brightly lit church, but I had to really pump the ISO at the reception because it was so dark. I left my regular flash at home since I have a baby and I didn't want to interfere with the pro photogs. Even at f/3.5 the images ended up so grainy (high iso) or blurry (slow shutter) that I ended up using my built in flash once the pros left. It really made me wish I had brought my DA 50 f/1.8 with me. (I don't even think my Tamron 17-50 f/2.8 would have been enough without flash.)
I do agree that you need to enjoy the event, but if you like things from your perspective I think it's entirely worth your time to spend a some 5-10 minutes in beginning, middle, and end taking a few memorable pictures, especially if there are no pros. In between you can even set your camera to full Auto and tell a few people to feel free to take some shots. I like the idea of letting a kid use it too since kids can take some wonderfully unexpected shots, but that also depends on how much you trust them with your camera.