I would say 12 is reasonable, only because they look so rich. On size alone, I would estimate 8 people (but my family likes cake)!
And this isn't your question, but I wanted to let everyone know that if you see a filling combination that you would like with a different character on the exterior, I was told that they are able to do that (ex. Pluto filling with Mickey exterior). They are not able to mix and match individual components of the filling, but you can swap out what it looks like on the outside.