For sure, and there is nothing wrong with these two at all - step sister is technically same as fucking a complete stranger, they don't share dna - well not until he empties his balls into her!! Family sex is way more prevalent than people realise.
I'm curious too what are their names. Those people should post more on they got great energy especially just next to each other well they were being interviewed.
Some details but basically whenever they get together having sex with each other is expected. Kind of a natural reaction when they get together. Mom and dad do not live close to bro and sis. bro and sis do not live close either. So they get together for big occasions - holidays and such - and they all have sex then at some point.