Hello there 
You did not specify if you wanted local or online multiplayer.
Still this is how i set up the winning conditions in my local multiplayer game.
Inside each player BP make a Bool variable that will be set to true if the player gets the trophy.
Then inside your “GameMode” BP Make an event tick.
Forget the first branch i’ve got in the picture.
Cast to each player and get the Bool variable that you have set to true for getting the trophy and then just put anything you want to happen after that. but keep in mind that you need the first “Do once” node that i have at the end of the player 1 cast otherwise the winning condition will keep executing every frame.
