Its probably a false claim to the throne to add some drama, the others will refuse to follow this other ShinkenRed and she'll be proved a false claimant and go away. Or it could be that Kaoru is a cousin and she actually is meant to be next Lord, but only if Takeru is dead or unable to fight. Also if Genta could create his own Shinkenger powers, then anyone just as smart and with knowledge of the Shiba Family and Shinkenger, could do the same.
As for the Takeru reveal, I always thought it might be revealed that Takeru was adopted by the Shiba Clan. It wouldn't make him a liar or any less the son and true 18th Lord of the Shiba family, but it would add a layer to his character and explain a lot of his somewhat schizotypal behavior.
Still it'd be kind of pointless to introduce such game changing plot twists this late when they can't really do much to explore how it effects everybody involved if it is the truth. It would be such a waste of a rich storyline that could have been explored throughout the series. :disappoin