You could just look at your screen.
If you have a person targeted, they will get a circle around their feet as a highlight… Other than that just check the enviroment around you and you see who you can run in range of(and raid frames should tell you who are in range, and who are not).
That should be all you need. If you can’t see that, I am not sure an addon will help you, 'cause the game basicly tell you where people are.