angle(Player(0).x, Player(0).y, Player(1).x, Player(1).y)
Or you add two temporary variables tempX, tempY, pick the first Player instance, set tempX=Player.X, tempY=Player.Y
Then pick the second player instance and use angle(tempX, TempY, Player.x,Player.y)
Or you can create a family with Player object, then you'll be able to pick Player and PlayerFamily in the same event and do angle(Player.x,Player.y, PlayerFamily.x, PlayerFamily.y)