geneticaly, yes. however, just seeing the mother for the first time it feels like the characters are meant to be taken as much younger. this would still be statutory rape and some jurisdictions know incest even with step- and adopted family aside from this.
ok sure legally some places think step-cest and incest are the same, if that case why not jjust make them full blood family? the only real reason someone makes them step-family is because the implication is that they aren't blood so therefore are fuckable. Step-family is only really used as a cheap work-around for avoiding incest. If we call both incest than there is no point to the work-around and they might as well have made it what it is, actual incest.
To sum it up, (a bit of speculation) i think the creator make them step-family in order to avoid actual incest (probably for legal reasons) and so it shouldnt be tagged as incest seeing as it's avoiding blood relation for that exact reason
Edit: Also age has nothing to do with incest, and the characters all look of legal age to me >_>, just cause they didnt make the mom with wrinkles and saggy tits doesnt mean she's too young to have adult kids, it just means the creator is sacrificing realism for what they think to be a more attractive character
