Adding the MB's will both work for and against shares. Any MBs associated with a reservation will automatically show up across accounts. However, it act's like having the same pictures tagged to two PP cards. So everyone can see them, but edits don't carry across from account to account. So Mom buys the Archive CD with her account. The pics from her band, Dad's band, Sally's band, and Johnny's band will show up in all 4 accounts (assuming each has their own
MDE/disney.com account). But if Dad makes edits, the edit's won't show up in Moms account. So in this scenario, it's not a huge deal as all 4 live in the same house, so they just need to make sure Mom does all the edits. However, if Grandma and Grandpa, or Neighbor Tom add their Magic Bands, then thats a different story. Since your Photopass account is now tied to your MDE/Disney.com account, sharing credentials is suddenly a big deal. Before, worst happens is someone changes your password, or orders the CD on accident. However now, they can change anything in any part of MDE/Disney.com. So they could theoretically change your existing reservations, make new ones, modify trip plans, etc. Tying Photopass into your MDE/Disney.com account now has much greater ramifications for account sharing that worrying about getting different bands added to your account.