How come Mulan, Elsa and Merida are considered Disney "princesses"?

How come Mulan, Elsa and Merida are considered Disney princesses?

Mulan married a warrior who as far as I remember is not related to the emperor?

Elsa is a queen. By incldung her they should have had to exclude most of the other princesses.

Merida is Pixar, they didn't even include all the actual Disney princesses 🤷‍♂️

Other Disney princesses:

-Bambi's wife

-Tiger Lily (she is just as much a princess as Pocahontas)

- Maid Marian (I think. She has to be related to Richard and John for that outlaw as an inlaw joke at the end of the movie to work)

-Eilonwy

-Ariel's sisters

-Nala

How come Mulan, Elsa and Merida are considered Disney "princesses"?
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