There is nothing wrong with organising in groups if that is done on a voluntary basis. We organise in families, people that have similar interests and so on. No violence required. Hierarchies are also fine so-long as the ones at the bottom can simply quit. Most people will not want to care about everything themselves and follow the lead of others they trust.

The NAP applies to everyone. With the people that reject the NAP the question is really about self-defence. You may react to violence, but not initiate it. The NAP is opposed to the offensive use of violence only. And anyone that takes the NAP seriously will obviously argue against using violence against people that reject the NAP, such political statists.