Not to sure about the uncle part, but I definitely think this is who Noct's father is referring to with the whole "you cannot have the throne" bit. If you remember the 2006 TGS trailer, where Noctis enters a room and there's a mage figure and both of them enter a standoff, I think that's him. And your right about the second and last picture. The last picture is just the CGI rendering of Noct's dad.