I'm GMing 2 tabletop Changeling campaigns at the moment. One of them takes place in Cambridge, while the other takes place in Inverness. As my birthday approaches, my players asked me to GM a session that will combine the 2 groups into a large one. The campaigns are taking place in the same world and some of the NPCs are actually identical so there is no story limitation.
A little bit about the groups
The group in Cambridge is made of 4 players with one playing an Elemental, 2 more playing Beasts and a Darkling. The second group is made of 5 players with one playing an Elemental, 2 who play Beasts, one who plays a Fairest and a Wizened. The players know each other and actually pass info about the scenes they like more between the groups so there's no point of misinform or bad chemistry.
A little bit about the campaigns
The campaign in Inverness ran for a few sessions more, but the difference in times is only a few days. It revolves around a safe house for the Lost and about the rise to power of the PCs. The themes of the campaign are "rise to power and the emotions of the seasons". The last session ended with a little bit of a catastrophe as an unidentified thing destroyed the main road of the freehold. One of the leaders of the Freehold is dead and the PCs are trying to fill the gap and to help the Freehold return to its proper and original form.
The Campaign in Cambridge is a little bit younger. It started with the creation of a motely of Lost who see themselves as a new kind of family and revolves around the formation of such a strong bond. The themes are "maintaining a functioning family against all odds and life as Lost refugees". In the second session the Freehold suffered from a Gentry attack and since then they're kind of on the run while still trying to stay in touch with the families that they originated from which they had to leave behind.
What I'm asking from you
Right now, I kinda know how to explain why they happen to be both in the same place (the kings and queens of the seasons are kinda friends) and I know where it should take place (in the freehold of Inverness). There's even a source for a conflict (the refugees sorta think that one of the characters from the Inverness freehold is the conspirator behind the Gentry attack). I do need, though, help in the form of tips about how to run it. Have you run a combined-group session? If so how did you run it? And most important of all (at least to me, anyway) what tips and ideas can you suggest for me from your experience?
Edit: Although I'll be glad for any tip or suggestion concerning this problem, there are 2 things that for me are on the head of my need list: 1) Pitfalls that I should avoid, and 2) Ways to sacrifice as little as possible from the personal feel of the campaign so far.