If I were to make guesses, I would say:
Because the Harley makes a distinction between a god and its servant, the serpent, it keeps me from saying something like Nidhog is a god.
Because the Harley mentions: Man killed the sun and became god, I have to assume that this is referencing either man harnessing technology or the descent of Nika into a devil fruit. With the preceeding part being the forest god tamed demons probably meaning the forest god created devil fruits, and the subsequent part being the sea god raged, I would surmise the Sea God has not been trapped in a devil fruit.
As for the forest god, it could be its the Forest God fruit, but it also might not be. I'm not going to say that "because its forest, it must have to do with plants" since Nika is associated with rubber. The critical linkage point is the taming of demons. Stuff like magic circles and glyphs, these are all tools that have to do with working together with demons, so saying the Forest God is doing this sort of magic is logically coherent.
Because the Sea Kings actively refer to Shirahoshi and one more as a "King," I do not believe Poseidon is the Sea God. Given that she is the daughter of Neptune, I'll say Poseidon is the daughter of a god. I'll say that the daughterhood "strips" the divine aspect for the purposes of One Piece.
I'm curious as to if there are more gods than the mentioned ones, because honestly, Oda could slot a bunch of the paramecia's as minor deities and I would accept it. At that point, though, I guess you could call demons minor deities, especially if you're handling the equivalents of presidents, maquises, dukes, and king demons.