I'm not sure this is the kind of question that someone who isn't a lawyer could answer for sure, but I don't think any offspring of currently powerful people would be alive in 120 years, and it's hard to imagine how the people in charge today are going to have a lot of offspring in their future, since most of them are older and past childbearing (if women) or past the age when they're likely to father children (if men, though there was James Doohan, who became a father at 80).
Is there a reason why these characters have to be the descendents of current well-known people rather than simply alluding to their being the great grandchildren, say, of undisclosed or made up early 21st politicians and billionaires?
Say, something like, "Bob was the great grandson of at least one prominent early 21st century billionaire on his mom's side, and of a mid-21st century US president and an infamous senate majority leader on his dad's (we all have eight great grandparents, so it would really bog you down to talk about all of them).