We here at Neatorama love great geek Halloween costumes, especially family ones, and this one might just be the best one we've ever seen not only for the quality of the costume, but also the subject matter.
Personally, I can't decide which is better though, the young Goblin King or the giant Ludo. Of course, Sir Didymus on his trusted steed is also pretty impressive, though and the girls are good too. Basically, Redditor Deconstructress nailed it.
Oh, and if you're wondering where Hoggle is, as one commenter pointed out, he's obviously the one taking the picture.