I don't know about Selvadorada, but I know in past when I've brought my sims friends to Granite Falls, I was not able to control the friends (without changing the household that I was controlling.) And said friends would actually sometimes randomly leave the holiday, I believe because they leave to go to work or school and then they return to their house instead of where they were staying. I don't know if this still happens, nor if it would be the same for Selvadora, but the day you book your sims holiday to Selvadorada I would advise booking time off work and school for both them and the friends they will be inviting. Hopefully then the friends won't leave the holiday randomly, although I can't be sure.
I suppose, besides switching the household you are controlling, you could also use the group feature to somewhat control what your sims NPC friends do.
