I have 34 MBs on my account and 18 cards, plus nearly equal amounts for 2 older kids and my DH, and a few for my 2 yr old toddlers. Our MBs do get wonky when we are there, and when bringing up that section on
MDE. I have all but 2-4 for each person marked as inactive, but we still usually have to spend a lot of time at the concierge desk getting the ones we want to use for that trip to work on the room, charging, tickets, elevators, etc. We have been told by a few CMs that you are only "supposed" to have 1 MB per person, but that's complete crap. When they tell me that I ask why Disney sells so many special ones, because they clearly don't want people buying one and never any more. They really can't answer that question. One time we were told something that made a little more sense, but I don't know IT so it might not make sense to people who do. They told my DH that everything you do in MDE is like a single "hit", and the more you have the more difficult it is for all of the programs to work, and work together (lots of paraphrasing and my interpretation there). So every ADR made, every ADR cancelled, every FP made, every FP changed, every MB, ever room reservation, etc. If that's the case we do have a TON, because I make and cancel LOTS of ADRS both before and during a trip, we have had quite a few stays and sometimes have changed resorts prior to the actual stay, do split stays, use refresh for FPe, etc. So if that's the case we do have a TON of "hits: on our account. But as much as we have, from reading here I know of plenty of people on these boards that would have more on their accounts, and they don't all have problems. So who knows.
FWIW, back to your original post, having 2 each should not be a problem at all. Even with Disney's system I don't think 2 per person could mess it up.