They're more like childhood friends rather than siblings, they were not raised by the same parents, they grow up and survive on their own
The example that i find uncomfortable is adopted siblings couple from "beware of the brothers" where FL is officially adopted, treated like a real daughter by the parents, and clearly were raised as siblings until the parents died in the accident, they're not blood related at all but the family bond is clear so i dropped that manhwa
But this one doesn't really feel like that, the father doesn't even raise his biological kids, the children see each other as killing target not siblings

Please no incest please no incest Please no incest please no incest