what? the worse kind of dudes are jealous harem-types.
no, their relationship is "open", they can do wherever they want with others.
the only one, (and this almost barely) that i could agree with, is Daughter, even if incest, theres an emotional connection, and if Father is true with Daughter (do not have relationships with other females) then, if Daughter has another male, now, we could start discussing cuckoldry.
Elena is a free spirit girl, and she liked it when old dude touched her, so theres nothing wrong here, and its definitely not cuckoldry or ntr.