...or they may have no real strengths at all!
(yes, I'm looking at you, DS3).
Or the bright ones may be lazyone emotional basket cases while the dim ones may be diligent charmers, so much more to it than brains.
Main thing I feel is to try to let them know that they are wonderful as they are. You are happy for whatever they achieve (no matter how small), and don't be happier for the high flyer than you are for the bumbling-along child. Try very hard to avoid "I'm proud" and instead try "Are you pleased with how you did?" "Wasn't that fun!"
They say you praise effort rather than results, too, but it's not always practical to do that, they will know that A* is better than B. Be practical, "What would YOU enjoy doing next?" not "It's too bad you didn't get such good results."
I know this one is in my future "I'm not so bothered exactly who got what result, I'm interested in whether you each really tried your hardest."
As you can see, We have to tiptoe around this kind of stuff.
My dad is one of 8 spread across 3 marriages, no certified geniuses but some with impressive academic records & prestigious careers and the others barely have any qualifications to their names, barely staying off of benefits. I dunno, they don't seem to have any self-esteem issues about it.