I can't recall any informed commentators being able to identify any logic or system of precedence in use at recent UK State events, our late Queen seeming to take quite an arbitrary approach. But it is a principle of international law that Heads of State are equal, taking precedence according to their length of service.

Hereditary monarchies also accord precedence to other hereditary monarchies. Luxembourg, Monaco and Liechtenstein, however, are no more junior to the Kingdoms than are the Kingdoms to the Emperor of Japan or, let's not forget, Empress Farah Dibah. I have never seen the Princes or the Duke bow to the Kings/Queens. I recall one occasion when Charlene curtsied (I'm sorry, I don't recall to whom), but it was much commented on (as being a faux pas).

If Albert attends he will break convention, but the sky will not fall in. That his father sent a representative to QEII's coronation, however, suggests that he was acting in the same way as a King would have. As to whether either Caroline or Stephanie would be suitable to represent their brother, their reputations are infinitely better than was that of their grandfather in 1953.