Yes, they are. But not as easy as that. Prinz is successor of his gramps, the Duke (because Eillete is saintess). Bia want to become head of her family, so she can't married into other family, she need a husband who is swordmaster but also have no title.
Prinz actually didn't support Eilette and Thesilid, he want his sister with his friend. But his friend also a heir of ducal family, and if Eilette marry him, her child will be his successor. But, if Eilette with Thesilid, their child can be named as her grandfather's successor so Prinz can marry Bia.
OHHHHHHHH Σ( ￣□￣)
Wow that's complicated lol
IS PRINZ N BIANCA OR BIA GONNA END UP TOGETHER??? (Just theory since she said she have to marry a sword/smaster ╥﹏╥ )