First player only does damage after second player has dealt damage, then first players damage works

Above is how my damage is working, My player shoots a line trace, tests if the hit is another player pawn, and gets the “damage resistance” on that player, my players damage is worked out by taking my “weapon damage”, and dividing it by the enemies “damage resistance”

Above is how my damage is applied in the event. the “Damage” float is my previously mentioned “Weapon damage” divided by the enemies “Damage resistance”

Float default values:
Damage Resistance : 2,
Weapon Damage : 10,
Damage : 0

Below is a video I uploaded to my problem, the first player only has his “Damage” float worked out after my second player has dealt damage.

That’s not how multiplayer works.
Unless you use a dedicated server, “first player” is the server, hosting the game. “second player” is a client.

Your trace function should be a function, not an input event. The function has to be executed on the server and the player has to request the server to execute this function.
You should read about replication, authority, etc.