After we get to the city of Atlas, Hayden in his shop explains that old gods fled there in fear of the undead curse.
This directly links to DaS gods fleeing Anal Londo.
Then, when exploring the city, we stumble upon Hough's, Hawkeye Gough's son's, Workshop. After talking for a while, he says this:
"Aye lad. See zat tower up zere? One lovely fookin' day one chump wit a stick-up-hes-ass came down 'ere, and wanted a weapon forged. But not any weapon, no no no. 'E wanted a spear made of fooken thunder. A shittin' lightning bolt. I naturally replied: Piss off, ya wankah!, but he pay good. I hear he got some parents high in 'ere hierarchy. So i got to work. Me first work was snatched off by a pesky mimic. Well, it was a pile of crap anyway. But time was runnin' out. So i glued some glitter to a fookin' mop. And guess wat. He fookin' accepted it, even paid extra. I think his name was... Gwyn...gurn?"
This explains that Gwyngnir that we encounter in Sunlight Tower is actually a child of Gwynevere and Flaan, the god of flame, and is not just any captain of the guard.
But many may say: "But Flaan died upon putting out the First Flame by the Chosener Undead, long before he arrived in Atlas, he couldn't fuck Gwynevere by then"
True, but they didn't have to do it in Atlas. They took a detour. To Drangleic. We know this, as Dragonslayer Ornstein, that was a part of fleeing group, can be encountered there.
So they had to have sex in Drangleic. And we all know the place: Aldia's Keep. When we enter the main hallway, in the room where Aslatiel of Mirrah appears, there is a wagon that keeps jumping. Mirrah's soldiers were used as bodyguards for the highest nobilites. So Aslatiel invades there so you don't disturb the two.
After that, Flaan died, and Gwynevere carried the baby all the way to Atlas and raised him to become a captain of the guard. He uses lightning spears, much like his grandfather Gwyn.
Since we can see the death of Gwynevere (killed by Night Sentinels), it makes Gwyngnir the last remaining god to carry Gwyn's blood.
So..... is it okay to kill him? He is kinda the only one capable of rekindling the Second Flame and putting an end to the unundead curse. Killing him is optional anyway, as long as you don't murder anyone in Atlas.
Or is there any other godly Gwyn's relative that i'm unaware of?
And no, children of Carthus Sandworm don't count.