Gentically, the would be indistinguishable from siblings…but they would still be geneological cousins.
EDIT - I should say “Largely indistinguishable.” A normal DNA test wouldn’t do it, but if you sequenced their whole genome, you would be able to tell which kid belonged to which couple because of random mutations. It would take a VERY BIG COMPUTER though.
as you can see i take this show very seriously
Just a 10 year old reeling in a fucking whale no big deal