Hi Carrie,
As soon as the Mickey's Not-So-Scary Halloween Party begins, the costume rules are relaxed for guests.
The rules state the following:
Costumes should be child-friendly and not obtrusive or offensive.
Adult guests may wear masks, but the masks must not obstruct vision
Guest who dress like Disney characters are not to pose for pictures or sign autographs for other guests.
Do not bring large or dangerous props with you.
Yes, both of you can dress up as Disney characters. You'll both make beautiful princesses. Have fun!