I was very late in remembering to post this, and then finally had a few seconds to catch JL online this morning. The guest-list has been expanded to include all the Weasleys at Remus' request. (Severus was keeping to only those he knew very well - and trusted to behave themselves, hence the twins did not make his list.)

Also, Remus knew Isadora throughout school while Severus didn't know her at all, so she's added.

So there are a few more people on the 'guest list' than what was there before. The full list can be found here with a P.S. that is only on the Twins' invites. ;)