If by "same skeleton" you mean that you have two characters in the same skin that have different bones, you simply change the draw order of the arms to be in front and behind the character receiving the hug.
If they share the same skeleton meaning there's only one character that has different skins, then I'd probably import the skeleton again to have a copy to look at. Animate the hug with the two of them, then I'd copy the animation of receiving a hug into the one giving it.
In unity there's a thing called skeleton separator that allows you to separate the arms and place another Skelton in the middle, if you're exporting spritesheets I'd probably make a third copy of the Skelton to have the hands visible above the other skeleton.
