Someone else had a similar question a week or so ago, and I think it was decided that this just too new to figure it out.
The credits are assigned to the room, so someone from each room would have to mobile order. Are the 2 with
MDE in the same room or different rooms? Will you all be eating together at every meal or will people split up at times? If you're eating together all the time, it won't matter that all the credits come from one or two rooms except.... Since you have 3 rooms, there is at least one room from which credits could not be subtracted unless someone in that room creates an account.
And I could have that completely wrong, but I'm pretty sure that's how it works.