Yeah, Brin and Natasha are married. When I'm not wrong I think their dojo is in Liverpool. I had the opportunity to practice with them a few times, since my master is a student of Brin and they both visit Berlin at least once a year, and I'm gonna tell you they are AMAZING! The way Brin teaches techniques is unbelievable, and he does something and downs his opponent, and you think "wow, that was amazing, I got it" he points to his feet and just then you realize he's got an oni kudaki with his feet.
I was amazed by both of them.
Next time I meet Brin I'm gonna ask him how he beat Ashida Kim, because I was told that's a pretty funny story
I haven't heard of any of your masters, but I'm not really that good in knowing people (hey, I love football but I know very few players).
Regards,
Il
PS: There is a belt system in ninjutsu, but it really is not that important