Your Sensei should have some idea of how the dojo is run. His students' kendo is a reflection of his kendo/teaching/understanding of the art. Therefore, he should have had a few words with the individuals in question else his kendo is the same as theirs then I suggest you find a new dojo My sensei has told me on many occasions if I come up with a kendoka (one in particular) who I feel like its not worth practicing with simply say no to the practice. Kendo is your hobbie and you should be enjoying it. and hey whats wrong with a kung fu or karate or boxer teacher?