I think Daniel siding with his dad was to show his mom that he's made his choice between his parents. He asked his mom about paying someone to beat the snot out of him to get him out of prison and she didn't deny it. That's just one of many things that he's found out about his mom. His dad, however, spilled the beans about a dark, dark secret without Daniel asking. Daniel may think his dad is the more honorable of the two (or at least the more open) and is willing to cast his lot with his dad and not his mom.
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