Who do JW's think is going to kill everyone at Armageddon?
Angels...humans are told to "stand still and see the Salvation of Jehovah"
How will it happen?
It starts with a Great Tribulation where the UN attack false religion and end up attacking JW's last, this is like attacking Jehoover and He comes via JC and the angels, probably using the natural elements too and systematically destroys all unfaithful humans.
What is their evidence?
It says so in the bible, according to their interpretation.
Who will be resurrected afterwards? Only JW's?
No, everyone prior to the Great Tribulation will be brought back those faithful first, then the unfaithful...barring a certain few like Adam & Eve, Sodom & Gomorrah etc