Board Thread:General Discussion/@comment-14610890-20140623051519/@comment-3146930-20140623092843

Yup, Monty confirmed this is not the case. However some of the things that lead people to think this is that they both wear red, similar color hair, she has power over fire and Yang has similar powers as well as red eyes (when her Semblance is active). Also people were hoping it would be this big reveal at some point down the road.

Here is an image with some of the reasons.