Apparently at some point they're referred to as "guardian gods," but what I think that may imply is like what you're saying; they're not really actual gods, but some kind of lesser deity. That's just how I see it, anyway.As for Termina, not much can be confirmed about that place. I don't believe the Four Giants are gods; more like protectors of the land in times of extreme crisis. Termina apparently takes place in an alternate universe or dimension, at least thats what I believe. Some think it takes place in another land. But that would mean it would be easily travelled to from Hyrule and probably be well known by other lands.
The Deku Tree and Jabu Jabu were referred to as "patron gods" or "patron deities" or something like that. So it seems that they are some kind of lesser deity or at least some kind of spirit.Like Dark_link01 said, I don't really think Termina has anything much to do with Hyrule. I don't think Termina has anything to do with the three Goddesses either, but I wouldn't call the Giants gods. They are more like the Deku Tree and Jabu Jabu, guardians of specific areas.
I'm not sure, but that might be referring to the four Light Spirits in Twilight Princess, but I don't think they're necessarily named after the Goddesses (though I will admit, the names are a little similar.) They four Light Spirits are: Eldin, Ordona, Faron, and Lanayru. The provinces of Hyrule in TP are also named after these Light Spirits.And what were these four light spirits named after the Goddesses that tried to kill Ganondorf?