I know it's likely not something I'm going to be able to find again, but I'm searching for a story I read years ago. There were multiple pairings, and I do mean multiple, and, of course, mpreg. I remember that Legolas was with Gimli and several of the elves were paired together, though I can't remember how exactly. Even Gandalf was in a pairing, if I recall, as were the hobbits. The main thing I do remember, is that it took place in Valinor, and it was extremely long, dozens of chapters in length.