Just a little remark: even if Snow and Charming and Thomas and Cinderella aren’t yet King&Queen, their daughters Emma and Alexandra are princesses. They automatically are, because at least one of their parents (or both actually) is a prince/princess.
Real life examples:
The infantas are princesses, even though Prince Felipe is not yet king. Prince William and Prince Harry are princes even though their father isn’t yet king. The princesses of The Netherlands, Denmark and Sweden also, etc. 😉