I'm in the same situation and am currently moving from the UK temporarily, trying to figure out the cheapest shipping option. I'm leaving most of my items in the UK in my home, which I'm renting, or in a storage unit. So, I only have a small amount of extra items, but too much to take on the plane. From what I've found online, it seems like using an excess baggage company or a shipping company (Fedex, UPS, DHL, etc) is the best option. It's supposed to be cheaper to send your extra items via a shipping company than it is to pay for extra bags. I'd definitely recommend leaving extra luggage with family members and having them bring the bags over when the come for the wedding. Leave your out of season clothing behind and have it brought over later. Clothing is actually much better in the UK, so you may find that you'd rather buy clothing here than have your items sent over.
When I moved over here I had 3 large suitcases and a sea shipment. I flew on United and BMI, and when I checked in, I wasn't charged anything for my extra bag, so that was a bonus. I think I just got lucky, though. I was fine only having 3 bags and waiting 5 months for the rest of my belongings.