What "4 modern presidents"?
Do they mean Russell - Rutherford - Knorr - Franz?
This is really confusing. Do they mean that because the lifespans of all 4 overlapped from 1905-1916, that that is "one generation"? And that "one generation" overlaps with the " current generation" of GB'ers? So you really don't have 2 overlapping generations, you have one smushed up overlapping set of multiple generations which overlaps with another smushed up overlapping set of multiple generations?
The problem with trying to understand something so awfully silly is you will never understand it because you don't have Jehovahs holy patented spirit to understand it. But I have a better idea if you want to understand it - and less time consuming.
Stick your head in a plastic bag and lay there for five minutes. If the brain damage is severe enough, you will understand it.