In the recently posted video about the religions of Westeros, GRRM points out that the first men adopted the Old Gods from the Children of the Forest. Martin describes the Old Gods as "the gods of the trees, the gods of the rocks and stones and mountains and streams, who had no names. there were no churches nor temples. There was no priesthood, and the symbol of them was the weirwood trees.."

We know that the First Men did indeed worship the Old Gods, because many old castles in Westeros still have a Godswood, even in the south where they worship the Seven. In fact, Harrenhal-- which was constructed after the Andal Invasion which brought the Seven to Westeros-- was built with a Godswood as well. Harren the Black was an Iron Islander so he was also, presumably, a worshiper of the Drowned God. That shows that the tradition of the Old Gods still has cultural importance in Westeros to those who now practice other religions.

However, one thing doesn't fit. I'm mentioning specifically the legend of the construction of Storm's End, in the Age of Heros. I will link the appropriate HBO lore video here, but also paraphrase the story below:

A warrior named Durran fell in love with Elenei, whose parents were the god of the sea and goddess of the wind. She becomes mortal to be with him, which angers her parents. During Durran and Elenei's wedding, the gods call a storm forth to destroy the castle and everyone inside. Durran and Elenei survive, and Durran declare war on the gods by rebuilding his keep. Each time he rebuilt the castle the gods would send a storm to tear it down, but Durran persisted. His seventh castle, Storm's End, withstood the storms of the gods. From there on, Durran became know as Durran Godsgrief, and became the first of the Storm Kings.

My issue is that Elenei and her parents do not sound at all like the Old Gods. First off, Elenei has a name. She may have become human, but she was at least godlike until she fell in love with Durran. Secondly, these gods have clear identities and personalities, while the Old Gods are supposed to be nameless spirits.

I this a separate mythology? If so, where did this religion come from? Did the people of the Storm Lands ever accept the Old Gods? And if the First Men already practiced a religion in westeros, why would they adopt the gods of the Children of the Forest?