One of the things I came across quite early on was The Tablet archive, this goes back to about 1840, and is great. When it covers weddings they list all the principal guests, and often what the wedding presents were.
Working on the basis of friends and family at both, it does give some very good hints, and throws up some intriguing links, and some very odd coincidences.
It certainly helps with the O’Bryens, Purssells, and Leschers. My plan is to slowly work through all the ones currently posted to see if I can get a better picture of who’s who, and whether they are friends or relations. I think I’ll keep the annotated versions private at the moment, but I’m happy to add users – just ask.
The weddings I’ve found so far are in no particular order.