Head into any multiplayer mode and then press and then to enter the outfitter. You will find Red and Pig Josh within the Red Dead Revolver menu. Once you have selected which character you want to use, proceed to a public/private freeroam or Legends and Killers playlists.
Select Red from the Red Dead Revolver multiplayer menu then head into either a public/private freeroam or Legends & killers playlist and hunt for the deadeye refills. You can always spot deadeye refill crates as they are marked with a green marker on your mini map. Once you have Have your deadeye ready to use, either hunt other players or a friend and click the to use deadeye. Lock onto them and kill them. Repeat this until the achievement unlocks.
Much like Red you will find Pig Josh in the same multiplayer outfitters menu. Head into a public/private freeroam or Legends playlist. Equip your dynamite located in the top left of the weapon wheel and kill 25 other people. Most games modes don't have dynamite in the levels so I suggest you do this in the free roam sections as you will start off with dynamite in your weapon wheel if you have unlocked it.
Note: To unlock the dynamite for Pig Josh or any other character, you need to reach level 15 to unlock this weapon.