From Shake it Up, are Gunther and Tinka supposed to be brother and sister?

I was watching the Shake It Up marathon one night because I was pretty
bored and I noticed that there is one part where Tinka wants to get a
boyfriend and Gunther is shocked when she says she doesn't want to
marry him. I thought they were supposed to be siblings?

There's also another part in an episode where Gunther talks about
"adolescent changes" and he makes a puppet say "I'm growing yarn in
places I haven't grown yarn before"

Aren't both topics kind of innapropriate for a show aimed at little
kids? First off with incestual marriage and also pubic hair?

(Though I did find the pubic hair thing funny, lol)