This show clearly wants to seem two things: smart and creepy. Don’t think it accomplishes either.
For being smart it wants us to close our eyes on quite a few things. Pretend things are not there, pretend other things make sense. But most importantly, it wants… No, it NEEDS us to believe people in this world are plain stupid or blind. Or maybe both.
One of the twins is always hiding and most of the time kind of in the open and close to the other one. Even if we assume the hiding twin is not visible (and there was a moment, when dad should have noticed him for sure), there is a thing called “presence”, we can feel people around us, especially during stress and adopting a child is stress. Even if we ignore that, they sometimes speak for each other, and that… They will sound different because of their placement, that would be noticeable. Let alone big box transporting one of the twins, and then one of them hanging birdhouse, while covering dad’s eyes with both hands… Those can’t be missed like that.
As for “creepy”… Well, it is creepy, but I think it’s creepy in a way different from what was intended. I think it’s the parents that make the show creepy somehow.
The only thing that would make all of these things make sense is magic, but it does not look like there is magic in this world.