Joe's dad is actually... *SPOILERS*
...dead, right?
Fin and Olivia have suffered losses. He's supposedly the only one who hasn't.
But we never see Joe's dad. When talking about him, Joe usually has to leave - maybe, like Olivia, he doesn't want people to see him break down? When his "dad" calls, Joe talks in another language - we really have no clue who he's talking to.
Then there's the part where Joe and his dad are going to meet Fin. Joe invites Fin and is surprised when Fin says yes. Hours later, Joe and his dad are no shows. When Joe is describing what happened,it sounds as if he's making up something.
I think Joe's dad is dead.