Well, yeah he should have some type of "family" since someone had to give birth to him. I mean more like he was abandoned, ran away, ignored, etc... such that he effectively never had someone taking care of him like the others.
I'm still wondering when Eunyung's backstory will be revealed. It's weird that there's a whole arc dedicated to him, but we didn't really get any insight to why he was living on that tent and why he developed quite a warped personality.