Each team member will have to live by them. Set consequences for missing meetings. It can be as trivial as making the non-attender take minutes for the next two meetings. It can be as extreme as expulsion once someone misses a specified number of meetings. Whatever you decide, stick to it.
Exceptions become the norm.
Late is wasteful. If six people have to wait 10 minutes for someone to show up, that's an hour of work lost. This may sound impolite, but it is the late-comer who is being rude. The idea that a negative comment or criticism might be repeated to someone outside the team can have a devastating effect on creativity. Remember the team is engaged in an on-going process.