2 Teams Score NOT Working !

I'm making a multiplayer game and want to make a Score system for both teams , so if you kill an enemy your team's score adds one point and so on...

all the methods i tried it either added one point and Only showed at the dead player's score (didn't show at any another player's score) , or it added on the dead player's score and kept adding.

Can someone please help and show me the code needed or the idea?
Thanks a lot !