I've just started trying to learn all this but it seems so many differences from site to site. For example one site I found said Leto was Zeus' wife? And in regards to Rhea having had Zeus, another site said he is from Coeus&Phoebe? That site showed a family tree, dont know how correct tho.
I can't wait to see a tree history page here, might make it less confusing.
you are perfectly right, because there is not one single version about the gods and their stories. We know about them from the ancient Greek literature, but from this literature only bits and pieces remained. The different writers wrote different stories about one and the same god.
As regards what you said, Leto was one of Zeus' lovers, not his wife. And in fact she was the daughter of Coeus and Phoebe. Zeus was married to Hera at that time, and when Hera found out about the pregnant girl, she forbade all the earth from giving shelter to Leto (I couldn't find other versions about this story, so I suppose the site where you found that information didn't have the facts quite right).
There was also another reason for the existence of the different versions: ancient Greece was formed by city-states, and each writer wanted his city to appear as the birth place of a certain god or the place of certain events. Also, many kings and princes wanted to prove they were great-great-grandsons of a god (and mainly Zeus'), that's why there are so many different versions about his love affairs and his children.
For instance, we all know that Aphrodite was born from the sea foam, but there is another version about her being the daughter
of Zeus and Dione. Aphrodite had an oracle at Dodona, in an oak-grove. That oracle was later used for worshipping Zeus, and so the story about Aphrodite being Zeus' daughter appeared.
Sometimes the ancient Greeks gave their gods characteristics borrowed from gods in other religions, or they would "adopt" a foreign god/goddess and adapt him/her to their culture, also changing his/her story. Other times, they tried to interpret a myth which was old even in their time and which was not logical for them, so they tried to find an explanation and thus changed the original myth.
There are also stories which are similar, but the characters change. For instance, in Persephone's case, Zeus decided that she should spend three or four months a year (depending on the version, of course) with her mother and the rest with her husband. When Persephone takes care of baby Adonis and doesn't want to give him back to Aphrodite, Zeus decides that he should spend one third of the year with Persephone, one third with Aphrodite and one third with whomever he chooses. The two stories are quite similar, right?
And of course, still speaking about Persephone, she was either Zeus' daughter or Poseidon's...
So in the end we can say that the different versions are all "correct", as there is no official "manual" of Greek mythology. They are stories told throughout the centuries and, as such, they were subject to change.
I'll start adding the family trees of the gods as soon as I figure out how to make them... but of course, there should be different family trees corresponding to the different versions about a god's family ^_^ Otherwise, in come cases, someone might turn out as being his own grandpa!