Regarding Rank Challenges

I didn't see anything in the guidebook about this or in the help desk so forgive me if I skipped over it! 

1) Are we required to seek OOC permission before challenging for a rank? 
While I personally have no issue with my characters being unexpectedly challenged, I can understand if a player would like a heads up. 

2) Can there be more than two participants in a rank challenge?
For example, could Wolf A challenge Wolf B and Wolf C jumps into to assist one of them.