It's the first time Pekka calls her his grand-daughter. As far as Seppo is concerned, she's officially his family.
Seppo has a point: the Amicale probably won't want a hybrid to live on "their" island. But between forcing oneself not to care or stopping the Amicale, they made opposite choices.
Poor Pekka. It's so frustrating when doing the right thing is a struggle.
Even more so since Pekka is a bit of a coward. It's not hard to yell at his friend when he knows he won't hurt him, but next to big mean human gangsters, it's a lot more difficult!