I also would say Talos is a god.
There is some evidence to suggest he is not the only mortal to enter godhood within the Nine. According to one of two possible explanations for the origin of Arkay, he may have been a mortal before rising to godhood as well. Here's a snip for UESP on the origin of Arkay:
'There are two legends about Arkay's origin. The book Ark'ay the God of Birth and Death has it that Arkay was once a regular shopkeeper with a passion for knowledge. He found a book written in a strange language and spent years upon years attempting to decipher it, slowly ignoring everything and everyone else around him. Eventually Arkay realized the book explained life and death itself, but by this time was at death's door with an incurable plague. Praying to Mara as a last resort, Arkay asked for more time to interpret the book. Mara gave him a choice: die now or become a god for eternity, charged with keeping the balance of death and life in the universe. The alternative is contained in The Monomyth, which suggests that Arkay was one of the very first spirits to "crystallize" after the start of time.'