Ryouma's Dad only live to forge katana, he doesn't want a family because that would hinder him from making katana. But, he was required to have a wife and a son to continue the family dojo. So when he was "given" a wife and a son, he only fulfills the bare minimum responsibilities like house, clothes, food and Ryouma's education until Ryouma is capable to be his own man.
For the God of Earth's behavior, nothing was ever confirmed. He did it on a whim, so to speak. The other clue is every otherwolders from Earth have a growth spike that will affect their magical, mental and physical abilities. This growth spike is caused by the God of Earth's influence, maybe he wants to take over Sailfall using the otherworlders. Yep, in short, he's an asshole.