When the hunter is killed? What should I do to kill another hunter?
Depends on the client used. Check out the links in OP (all of them, e.g. "Old Version Huntercoin" mega link has a text with game rules)
Can I kill a hunter in a 1 vs 1 fight? Do I have to more hunters?
Yes, it's possible, but like in fencing, 2 against 1 gives better chances.
There is definitely a need for some documentation for Huntercoin game play.
There was a bounty released a bit back for it
...
Someone can probably get the bounty by collecting all relevant infos from this thread, including how much coins this bounty was (5k iirc)