Alas, there really isn’t any way to stop people taking photos and posting them up, it seems to go with the territory these days. I’ve done as the poster above suggested and asked everyone to take their photos after I’ve taken mine. It even works sometimes! The rest of the time people will look at me like I have three heads, and take their photos anyway.
As for your situation, your version of the photo is by far superior to the other one, and despite them being taken at roughly the same time, I think yours looks totally different to theirs, with the angle, the lighting, the colours and the fact that the bridal party are all looking at you. Once you release your photos, the bride et al will be able to easily see how much better your pro shots are. I understand your frustration with the other ones being posted up, as that sort of thing annoys me as well. It’s just one of those things which cannot be controlled, and when it comes down to it, as long as I’ve been paid, then I’ll deal with it, lol!