As much as I would like a party of 6 so a custom character and all of the origin characters can be there, I get it if its about balancing.
However 5 could work, if 6 is too much, and multiplayer can be 4 and then they can bring 1 origin character, that way if they have any unique quests or such they can still be there.
I believe Larian said something about having a solo mode where its just a party of 1, they might do a thing for adjusting encounters on party size.
