This is really difficult. I am a yoga teacher, however my husband and son dont do yoga regularly. Till my son was 8-9years he did it watching me, but last 4-6years he was more into football like my husband.
Now at 14, he just told me yesterday that he will do yoga in the summers. I think his hamstring inflexibility and stress from exams was the trigger. Of course I was overjoyed.
Husband though - i think he just needs the right teacher. He did it for 2-3 months, but didnt continue after the teacher left.