I'm not sure, but what with the way Tamas are programmed I think not. Your V5 is programmed in numbers - so for example Kuchipatchi might be number 0467 and Yonepatchi is 0468. It is programmed to "think": If player has 0467 and marries external 0468 then that = pure family.
No, but if you marry your Yonepatchi to a Kuchipatchi, you might get an "Easygoing Family" in your name plaque, instead of "Blended Family." If this happens, you will get 1 or 2 characters on the next generation. What I did a while ago: had blended family, got easygoing family through marriage, then got a Kuchipatchi in my easygoing family, then married Yonepatchi and got the Kuchi Family.