Do you think House Jordayne could be a cadet branch of House Dayne of Starfall?

Well, the name similarity would normally suggest that, but in this case, we know differently. House Jordayne is named in honor of the late Robert Jordan, sci-fi and fantasy author – its castle, the Tor, is named after Jordan’s publisher, the current lord’s first name is Robert spelled backwards, its sigil is a pen, etc.