dragon warriors

It would just entail proving their worth and loyalty to them,  and that can be done in many ways,  usually by showing their best skill.  Also requires them to at least like the one trying to join,  otherwise it'd take a lot more proving. They have to be willing to accept their beliefs and 'religion' as well as drop all their other beliefs and religion should there be any.  Those that practice other beliefs and religions are seen as a threat when they're a part of the clan,  but they don't care what anyone who's not part of the clan does. They're not gonna run around and preach it to everyone, but they expect those who join to follow their ways.